The copy of the original arguments of a aggregate function was not
initialized until after fix_fields().
Sometimes (e.g. when there's an error processing the statement)
the print() can be called with no corresponding fix_fields() call.
      
Fixed by adding a check if the Item is fixed before using the arguments
copy.

mysql-test/r/explain.result:
  Bug #43354: test case
mysql-test/t/explain.test:
  Bug #43354: test case
sql/item_sum.cc:
  Bug #43354: use the argument list copy only if it's initialized

The method to purge binary log files produces different results in some platforms.
The reason is that the purge time is calculated based on table modified time and
that can't guarantee to purge master-bin.000002 in all platforms.(eg. windows)

Use a new way that sets the time to purge binlog file 1 second after the last modified time of master-bin.000002.
That can be sure that the file is always deleted in any platform.

mysql-test/suite/rpl/r/rpl_rotate_logs.result:
  Test result
mysql-test/suite/rpl/t/rpl_rotate_logs.test:
  Change 'purge time' 1 sencond after the last modified time of master-bin.000002.

Changes are due to changes in precision.
Re-record of .result files to account for new server precision.

test-fixes for 32-bit

mysql-test/t/variables.test:
  Test for 10351 ("Max_Heap_Table_Size cannot be set to 4 gb")
  now throws a warning on 32-bit, as it should. As we're not
  actually interested in the warning but only in whether the
  variable is set to a correct value afterwards, we disable
  warnings for the duration of that test case so we won't have
  to split the test into a 32-bit and a 64-bit flavour for no
  real reason.

When disk is full, server may waiting for free space while
writing binlog, relay-log or MyISAM tables. The server will 
continue after user have freed some space. But the error
message printed was not quite clear about the how often the
error message is printed, and there will be a delay before
the server continue and user freeing space. And caused users
thinking that the server was hanging forever.

This patch fixed the problem by making the error messages
printed more clear. The error message is split into two part,
the first part will only be printed once, and the second part
will be printed very 10 times.

Message first part:
Disk is full writing '<filename>' (Errcode: <errorno>). Waiting
for someone to free space... (Expect up to 60 secs delay for 
server to continue after freeing disk space)

Message second part:
Retry in 60 secs, Message reprinted in 600 secs

                          
When using mixed mode the record values stored inside the storage
engine differed from the ones computed from the row event. This
happened because the prepare_record function was calling
empty_record macro causing some don't care bits to be left set.
                          
Replacing the empty_record plus explicitly setting defaults with 
restore_record to restore the record default values fixes this.                          

Some changes that make things more elegant in 6.0,
backported so the code is mostly the same in 5.1,
for easier maintainence.

sql/set_var.cc:
  Backporting some changes to 5.1 so the code is
  mostly the same in both versions. Less to learn!

modifications according to the reviews are included

This is a back port from 5.1 to 5.0.

Fix for BUG 20023: mysql_change_user() resets the value
of SQL_BIG_SELECTS.
  
The bug was that SQL_BIG_SELECTS was not properly set
in COM_CHANGE_USER.
  
The fix is to update SQL_BIG_SELECTS properly.



sql/sql_class.cc:
  Update THD::options with the respect to SQL_BIG_SELECTS
  in COM_CHANGE_USER.
tests/mysql_client_test.c:
  Add a test case BUG#20023.

      
When binlog_format is STATEMENT and the statement is unsafe before,
the unsafe warning/error message was issued without checking
whether the SQL_LOG_BIN was turned on or not.
      
Fixed with adding a sql_log_bin_toplevel flag in THD to check
whether SQL_LOG_BIN is ON in current session whatever the current is in sp or not.


mysql-test/suite/binlog/r/binlog_unsafe.result:
  Test case result for unsafe warning/error message
mysql-test/suite/binlog/t/binlog_unsafe.test:
  Test case for unsafe message warning/error
sql/set_var.cc:
  Adding a function set_option_log_bin_bit() which specailly handles to
  the change of SQL_LOG_BIN bit in order to set sql_log_bin_toplevel
  according to SQL_LOG_BIN current value at the same time.
sql/sql_class.cc:
  Initialize the flag sql_log_bin_toplevel in THD::init(),
  and add the condition to check whether unsafe ror message was issued.
sql/sql_class.h:
  Add a sql_log_bin_toplevel flag in THD to indicate whether the toplevel SQL_LOG_BIN is

set user variable max length on
fix_length_and_dec() stage
using real value length.


mysql-test/r/variables.result:
  test result
mysql-test/t/variables.test:
  test case
sql/item_func.cc:
  set user variable max length on
  fix_length_and_dec() stage
  using real value length.

The problem was that the server was trying to use the unknown
error format string (ER_UNKNOWN_ERROR) to print messages about
comments being too long, but the said format string does not
accept arguments and will always default to "Unknown error".

The solution is to introduce new error messages which are
specific to the error conditions so that server wants to
signal -- this also means that it's possible to translate
those messages.

mysql-test/r/strict.result:
  Update test case result.
mysql-test/t/strict.test:
  Update test case with new errors.
sql/share/errmsg.txt:
  Introduce new errors for long comments.
sql/unireg.cc:
  Use new errors.