WL#5142 FLUSH LOGS should take optional arguments for which log(s) to flush

Support for flushing individual logs, so that the user can
selectively flush a subset of the server logs.

Flush of individual logs is done according to the 
following syntax:

  FLUSH <log_category> LOGS;

The syntax is extended so that the user is able to flush a
subset of logs:

  FLUSH [log_category LOGS,];

where log_category is one of:
  SLOW
  ERROR
  BINARY
  ENGINE
  GENERAL
  RELAY.

include/mysql_com.h

@@ -115,6 +115,12 @@ enum enum_server_command
 					   thread */
 #define REFRESH_MASTER          128     /* Remove all bin logs in the index
 					   and truncate the index */
+#define REFRESH_ERROR_LOG       256 /* Rotate only the erorr log */
+#define REFRESH_ENGINE_LOG      512 /* Flush all storage engine logs */
+#define REFRESH_BINARY_LOG     1024 /* Flush the binary log */
+#define REFRESH_RELAY_LOG      2048 /* Flush the relay log */
+#define REFRESH_GENERAL_LOG    4096 /* Flush the general log */
+#define REFRESH_SLOW_LOG       8192 /* Flush the slow query log */
 
 /* The following can't be set with mysql_refresh() */
 #define REFRESH_READ_LOCK	16384	/* Lock tables for read */