Merge Percona Server 5.5 to MySQL 5.6

Merge Percona Server 5.5 to MySQL 5.6 to produce Percona Server 5.6.

Features to be merged:
extended slow query log
_STATS tables
InnoDB show verbose locks/locks held
--innodb-optimize-keys
kill idle txns
fake changes
query cache strip comments
query cache "Waiting on query cache mutex"
processlist rows_sent etc
dynamic sized rows in MEMORY
innodb_deadlocks (count)
--log-warnings-suppress
innochecksum file format detection
utf8_general50_ci
corrupt_table_action
adaptive_hash_cells etc
innodb_use_global_flush_log_at_trx_commit
INNODB STATUS extensions
innodb_log_block_size
Too many connections warning
NUMA
fixed size readahead
max_binlog_files
Lock-free SHOW SLAVE STATUS
PT UDFs
enforce_storage_engine
utility user
secure_file_priv
Expanded program option modifiers
changed page bitmaps
PAM plugin
userstat
syslog
I_S.TEMPORARY_TABLES and GLOBAL_T_T
XtraDB comment in show storage engines
Bug fixes