Minor cleanups, fix compiler warnings
Change MySQL -> MariaDB inc scripts
Changes for using build scripts

Removed -DSECURITY_HARDENED=OFF for debug build scripts
ignore configure
Made sql_log_slow a session variable

mysqldump:
- Added --log-queries to allow one to disable logging for the dump

sql/log_event.cc:
- Removed setting of enable_slow_log as it's not required anymore.

sql/sql_parse.cc:
- Set enable_slow_log to value of thd->variables.sql_log_slow as this will speed up tests if slow log is disabled.
- opt_log_slow_admin_statements can now only disable slow log, not enable it.

sql/sql_explain.cc:
- Minor cleanup

Other things:
- Added sql_log_slow to system variables.
- Changed opt_slow_log to global_system_variables.sql_log_slow in all files
- Updated tests to reflect changes