Replaced COND_refresh with COND_global_read_lock becasue of a bug in NTPL threads when using different mutexes as arguments to pthread_cond_wait()
The original code caused a hang in FLUSH TABLES WITH READ LOCK in some circumstances because pthread_cond_broadcast() was not delivered to other threads.
This fixes:
Bug#16986: Deadlock condition with MyISAM tables
Bug#20048: FLUSH TABLES WITH READ LOCK causes a deadlock


mysql-test/r/flush.result:
  Added test case for deadlock with FLUSH TABLES WITH READ LOCK
mysql-test/r/lock_multi.result:
  Test for bug in LOCK TABLE + optimize table
mysql-test/t/flush.test:
  Added test case for deadlock with FLUSH TABLES WITH READ LOCK
mysql-test/t/lock_multi.test:
  Test for bug in LOCK TABLE + optimize table
sql/lock.cc:
  Replaced COND_refresh with COND_global_read_lock becasue of a bug in NTPL threads when using different mutexes as arguments to pthread_cond_wait()
  The original code caused a hang in FLUSH TABLES WITH READ LOCK in some circumstances because pthread_cond_broadcast() was not delivered to other threads
sql/mysql_priv.h:
  Added COND_global_read_lock
sql/mysqld.cc:
  Added COND_global_read_lock
sql/sql_base.cc:
  More DBUG statements
  Added a broadcast in remove_table_from_cache() to release any threads waiting in open