MDEV-82 : Fix place in thr_lock.c where wait-end callback was called without corresponding wait-begin

Allow for faster creation of threads in corner cases where pool would be overloaded with long non-yielding queries. 
To allow it, change minimum of thread_pool_stall_limit to be 10 milliseconds.

Also introduce a new parameter to oversubscribe a group . Number of threads running in  parallel would be higher than it normally should, leading to thrashing, but it may improving preemptiveness, which is useful for the described corner case.

Note: to build with -fno-rtti as we currently build the server, boost version  1.45 or later is required.
(without -fno-rtti, 1.40 is enough)

LP909512: Fix crash on tp_set_threadpool_size if threadpool is not used(thread_handling != pool-of-threads)

Fixes valgrind warning.

Fix oqgraph build . Plugin does not need rtti, and does not load if rtti compile settings are different from server's

Fixed memory leak printing when doing 'mysqld --version', 'mysqld --debug --help' and 'mysqld --debug --help --verbose'


mysys/my_init.c:
  Moved checking if we should call DBUG_END() before my_thread_end() as otherwise we will not free DBUG variables and files.
mysys/thr_lock.c:
  Fixed compiler warning
sql/mysqld.cc:
  Fixed memory leaks when using mysqld --help and mysqld --version
  Added --debug as an option that works for all builds. For non debug builds we now get a warning.
strings/dtoa.c:
  Fixed valgrind warning (c could contain data outside of the given string)

Patch by elenst

Contributed by Maarten Vanraes (AL13N)

Fix things so that chains of certificates work in the server and client
certificate files.

This only really works for OpenSSL-based builds, as yassl is unable to read
multiple certificates from a file.  The patch below to yassl/src/ssl.cpp
doesn't fix that, but just arranges that the viosslfactories.c patch won't
have any ill effects in a yassl build.

it is a static library that links with shared libraries, so strictly speaking it should
have -fPIC or equivalent flags. Also, it must always build as static no matter
whether  BUILD_SHARED_LIBS is set.

that caused the default value to be written into an arbitrary location inside
global_system_variables

* MYSQL_MAINTAINER_MODE and SAFEMALLOC take values ON/OFF/AUTO
  (in all builds, in none, only in debug and platform dependent)
* ./configure prefers RelWithDebInfo unless the user overrides

(and to follow the naming conventons).
keep old debug variable, but mark it as deprecated.