The variables now return real values. They can't be made usual variables because they do not have DEFAULT value.

Removed MDL map partitions. Won't be needed when this MDEV is implemented.

Removed MDL objects cache. Won't be needed when this MDEV is implemented.

query_prealloc_size, query_alloc_block_size and log_tc_size.

Fixed incorrect registration of LOCK_binlog_end_pos in PFS.

Extend existing plugins to support
* SHOW QUERY_RESPONSE_TIME
* FLUSH QUERY_RESPONSE_TIME
* SHOW LOCALE

move userstat tables to use the new API instead of
hand-coded syntax

INFORMATION_SCHEMA.SYSTEM_VARIABLES