MDEV-6109: EXPLAIN JSON
- First code, "EXPLAIN FORMAT=JSON stmt" and "ANALYZE FORMAT=JSON stmt"
  work for basic queries.  Complex constructs (e.g subqueries, etc) not
  yet supported.
- No test infrastructure yet
Raise version number after cloning 5.5.39
BUG#18779944: MYSQLDUMP BUFFER OVERFLOW

Mysqldump overflows stack buffer when copying table name from commandline arguments resulting in stack corruption and ability to execute arbitrary code.

Fix: Check length of all positional arguments passed to mysqldump is smaller than NAME_LEN.
Note: Mysqldump heavily depends on that database objects (databases, tablespaces, tables, etc) are limited to small size (now it is 64).
Bug#17873011 NO DEPRECATION WARNING FOR THREAD_CONCURRENCY

Description:
THREAD_CONCURRENCY is deprecated and there is no 
deprecation warning message while setting this variable
while starting the server.

Analysis:
This variable is specific to Solaris 8 and earlier systems
and is ignored on all other platforms. But since many 
customers, who uses other than Solaris, still has this 
variable in their configuration file, it is important to
have a deprecation warning.

Fix:
THREAD_CONCURRENCY deprecation warning message is added.
Bug #19140907 DUPLICATES IN UNIQUE SECONDARY INDEX BECAUSE OF FIX OF BUG#68021

Problem:

When a unique secondary index is scanned for duplicate checking, gap locks
were not taken if the transaction had isolation level <= READ COMMITTED. 
This change was done while fixing Bug #16133801 UNEXPLAINABLE INNODB UNIQUE
INDEX LOCKS ON DELETE + INSERT WITH SAME VALUES (rb#2035). Because of this
the duplicate check logic failed, and resulted in duplicate values in unique
secondary index.

Solution:

When a unique secondary index is scanned for duplicate checking, gap locks
must be taken irrespective of the transaction isolation level.  This is
achieved by reverting rb#2035.

rb#5910 approved by Jimmy
Bug#18469276: MOD FOR SMALL DECIMALS FAILS
      
Problem:
If leading zeroes of fractional part of a decimal
number exceeds 45, mod operation on the same fails.
      
Analysis:
Currently there is a miscalcultion of fractional
part for very small decimals in do_div_mod.
      
For ex:
For 0.000(45 times).....3
length of the integer part becomes -5 (for a length of one,
buffer can hold 9 digits. Since number of zeroes are 45, integer
part becomes 5) and it is negative because of the leading
zeroes present in the fractional part.
Fractional part is the number of digits present after the
point which is 46 and therefore rounded off to the nearest 9
multiple which is 54. So the length of the resulting fractional
part becomes 6.
      
Because of this, the combined length of integer part and fractional
part exceeds the max length allocated which is 9 and thereby failing.
      
Solution:
In case of negative integer value, it indicates there are
leading zeroes in fractional part. As a result stop1 pointer 
should be set not just based on frac0 but also intg0. This is
because the detination buffer will be filled with 0's for the length
of intg0.

strings/decimal.c:
  Calculate stop1 pointer based on the length of intg0 and frac0.
WL#7219: Implement audit filter
Bug#18935421 RPAD DIES WITH CERTAIN PADSTR INTPUTS....

For rpad() and lpad(): verify that the padding string is well-formed.
BUG#18942294 - SEGV IN DICT_FIND_TABLE_BY_SPACE TRYING TO MARK SPACE CORRUPT
IN RECOVERY

During redo log processing, the data dictionary is not available. We should
check it in dict_find_table_by_space() to prevent SEGV error.

rb#5678, approved by Jimmy.
Bug #19149091 5.5 BUILD BREAKS ON LINUX IF SUN DTRACE IS INSTALLED

  Add some code adapted from 5.6 to check for "real" DTrace. If found,
  and system is Linux, we simply set DTRACE to OFF. Otherwise no change.

  Build will still break if one tries to manually set DTRACE to ON.
Bug#19172145 - Remove perl(GD) and dtrace dependencies and bench fix
Bug#14757009: WHEN THE GENERAL_LOG IS A SOCKET AND THE READER
              GOES AWAY, MYSQL QUITS WORKING.

Analysis:
-----------------
Issue in this bug and in bug 11907705 is, the socket file or
fifo file is set for general log at command line while starting
the server. But currently, only regular file can be set for the 
general log. Instead of reporting any error, the provided files
are opened for writing and continued. Because of this issues
mentioned in the bug reports are seen.

As mentioned, only when any non-regular file is set for general
log at command line while starting the server, these issues are
seen. If general log file is set to non-regular file from CLI
using system variable general_log_file then error is reported.

These issues can also be faced with slow query log file, if it is
set to non-regular file.

Fix:
-----------------
Currently while starting the server if we fail to open log file
then we report an error, disable logging to file and continue.
To fix issue reported code is modified to check whether file
is regular file or not before opening it. If file is not a 
regular file then error is logged to error log and logging to 
file is disabled.
Bug #17297324 GLIBC DOUBLE FREE OR CORRUPTION WHEN KILLING CLIENT; CTRL+C 

Description: Sometimes when killing the mysql command line client with
KILL -2(SIGINT), mysql client core dumps as a result of a double free or
corruption.

Analysis: When we run the mysql client in command line mode it will goes
to mysql_end() and frees many data structures. At the same time (i.e
after some data structures are freed), if we give "KILL -2" signal then
the signal will be handled with function handle_kill_signal() and as
part of it will again calls mysql_end() and goes with free() to the
already freed data structure for batch_readline_end() function, which
causes core dump.

Fix: Ignoring SIGQUIT and SIGINT signals when cleanup process starts.
This will help in resolving the double free issues, which occurs 
in case the signal handler function is started in between of the 
clean up function.
For 5.6 we need to ignore SIGHUP also.
Bug#19223915 Provide mysql-compat-server dependencies
Bug #18384260: MULTIPLE SECURITY ISSUES IN CERTIFICATE VALIDATION

the 5.5 version of the fix.
Added a call to X509_verify_cert_error_string() into the client certificate
verification code.
Merge from mysql-5.5.39-release
Bug #18415196 MYSQL_UPGRADE DUPLICATE KEY ERROR FOR MYSQL.USER FOR 5.5.35+, 5.6.15+, 5.7.3+

Description: mysql_upgrade fails with below error, 
when there are duplicate entries(like 'root'@'LOCALHOST'
and 'root'@'localhost') in mysql.user table.
ERROR 1062 (23000) at line 1140: Duplicate entry 'localhost-root' for key 'PRIMARY'
FATAL ERROR: Upgrade failed

Analysis: As part of the bug 12917151 fix we are 
making all the hostnames as lower case hostnames.
So, this has been done by mysql_upgrade.
In case of above mentioned duplicate entries 
mysql_upgrade tries to change hostname to lowercase.
Since there is already 'root'@'localhost' exists.
it is failing with "duplicate entry" error.

Fix: Since its a valid error failure. We are 
making the error more verbose. So, that user will
delete the duplicate errors manually.
Along with existing error we are printing below
error as well.
ERROR 1644 (45000) at line 1153: Multiple accounts exist for @user_name, @host_name that differ only in Host lettercase; remove all except one of them
Bug #18415196 MYSQL_UPGRADE DUPLICATE KEY ERROR FOR MYSQL.USER FOR 5.5.35+, 5.6.15+, 5.7.3+

Follow-up patch. Removed unwanted code.