Backporting wl6715 to mysql-5.5

The types mysql_event_general/mysql_event_connection are
being cast to the incompatible type mysql_event. The way
mysql_event and the other types are designed are prone to
strict aliasing violations and can break things depending
on how compilers optimizes this code.

This patch fixes audit interface, so it confirms to strict-
aliasing rules. It introduces incompatible changes to audit
interface:
- mysql_event type has been removed;
- event_class has been removed from mysql_event_generic and
  mysql_event_connection types;
- st_mysql_audit::event_notify() second argument is event_class;
- st_mysql_audit::event_notify() third argument is event of type
  (const void *).

"Writing Audit Plugins" section of manual should be updated:
http://dev.mysql.com/doc/refman/5.5/en/writing-audit-plugins.html

include/mysql/plugin_audit.h:
  event_class has been moved out of mysql_event types.
include/mysql/plugin_audit.h.pp:
  event_class has been moved out of mysql_event types.
plugin/audit_null/audit_null.c:
  event_class has been moved out of mysql_event types.
sql/sql_audit.cc:
  event_class has been moved out of mysql_event types.

include/mysql/plugin_audit.h:
  Connection auditing class.
include/mysql/plugin_audit.h.pp:
  Connection auditing class.
sql/mysqld.cc:
  Notify disconnect to auditing.
sql/sql_audit.cc:
  Connection class event dispatcher.
sql/sql_audit.h:
  mysql_audit_notify() is not available in embedded.
sql/sql_connect.cc:
  Notify connect to auditing.
sql/sql_parse.cc:
  Notify user change to auditing.

            attempt to install a plugin twice

Server crashes when [UN]INSTALL PLUGIN fails (returns an
error) and general log is disabled and there are audit
plugins interested in MYSQL_AUDIT_GENERAL_CLASS. 

When audit event is triggered, audit subsystem acquires interested
plugins by walking through plugin list. Evidently plugin list
iterator protects plugin list by acquiring LOCK_plugin, see
plugin_foreach_with_mask().

On the other hand [UN]INSTALL PLUGIN is acquiring LOCK_plugin
rather for a long time.

When audit event is triggered during [UN]INSTALL PLUGIN, plugin
list iterator acquires the same lock (within the same thread)
second time.

Repeatable only with general_log disabled, because general_log
triggers MYSQL_AUDIT_GENERAL_LOG event, which acquires audit
plugins before [UN]INSTALL PLUGIN acquired LOCK_plugin.

With this fix we pre-acquire audit plugins for events that
may potentially occur during [UN]INSTALL PLUGIN.

This hack should be removed when LOCK_plugin is fixed so it
protects only what it supposed to protect.

No test case for this fix - we do not have facility to test
audit plugins yet.

sql/sql_audit.cc:
  Move "acquire audit plugin" logics to a separate
  function.
sql/sql_audit.h:
  Move "acquire audit plugin" logics to a separate
  function.
sql/sql_plugin.cc:
  Pre-acquire audit plugins for events that may potentially occur
  during [UN]INSTALL PLUGIN.

            e.g.MYSQL_AUDIT_GENERAL_ERROR

General audit API (MYSQL_AUDIT_GENERAL_CLASS) didn't expose event
subclass to plugins.

This patch exposes event subclass to plugins via
struct mysql_event_general::event_subclass.

This change is not compatible with existing general audit plugins.
Audit interface major version has been incremented.

include/mysql/plugin_audit.h:
  Expose event subclass to audit general plugins.
plugin/audit_null/audit_null.c:
  Added distinct counters for general event sub-classes.
  
  Removed printf() from deinit(). One can easily see number of
  calls via status variables.
  
  To make code nicer, modified class mask to use macro instead
  of hardcoded number.
  
  Incremented audit plugin minor version.
sql/sql_audit.cc:
  Expose event subclass to audit general plugins.

This patch:

- Moves all definitions from the mysql_priv.h file into
  header files for the component where the variable is
  defined
- Creates header files if the component lacks one
- Eliminates all include directives from mysql_priv.h
- Eliminates all circular include cycles
- Rename time.cc to sql_time.cc
- Rename mysql_priv.h to sql_priv.h

WL#3771
  "Audit Plugin Interface"
  Implement new plug-in type - AUDIT
  New plug-in: audit_null
    simply increments counter for how many times it was called.

include/Makefile.am:
  wl3771
    add new headers to distribution
include/mysql/plugin.h:
  wl3771
    define new AUDIT plugin type
    Split out fulltext plugin type into its own header
include/mysql/plugin.h.pp:
  wl3771
    no real API change, just re-arranged some code
include/mysql/plugin_audit.h:
  wl3771
    pluggable audit interface
include/mysql/plugin_ftparser.h:
  wl3771
    Split out fulltext plugin type into its own header
libmysqld/CMakeLists.txt:
  wl3771
    add sql_audit.cc to build
libmysqld/Makefile.am:
  wl3771
    add sql_audit.cc to build
plugin/audit_null:
  wl3771
    an example plugin for testing pluggable audit interface
plugin/audit_null/Makefile.am:
  wl3771
    an example plugin for testing pluggable audit interface
plugin/audit_null/audit_null.c:
  wl3771
    an example plugin for testing pluggable audit interface
plugin/audit_null/plug.in:
  wl3771
    an example plugin for testing pluggable audit interface
sql/CMakeLists.txt:
  wl3771
    add sql_audit.cc to build
sql/Makefile.am:
  wl3771
    add sql_audit.cc to build
sql/event_queue.cc:
  wl3771
    release audit resources before waiting
sql/log.cc:
  wl3771
    add general audit call for log
sql/mysqld.cc:
  wl3771
    add audit initialize/finalize
    add general audit call for error
sql/sql_audit.cc:
  wl3771
    pluggable audit interface implementation
sql/sql_audit.h:
  wl3771
    pluggable audit interface implementation
sql/sql_class.cc:
  wl3771
    add thd audit init/deinit calls
sql/sql_class.h:
  wl3771
    add required data structures for audit to THD
sql/sql_connect.cc:
  wl3771
    release audit resources before waiting
sql/sql_insert.cc:
  wl3771
    release audit plugins before waiting
sql/sql_parse.cc:
  wl3771
    add general audit call for results
sql/sql_plugin.cc:
  wl3771
    add declarations for audit plugin type