WL#5030: Split and remove mysql_priv.h

This patch:

- Moves all definitions from the mysql_priv.h file into
  header files for the component where the variable is
  defined
- Creates header files if the component lacks one
- Eliminates all include directives from mysql_priv.h
- Eliminates all circular include cycles
- Rename time.cc to sql_time.cc
- Rename mysql_priv.h to sql_priv.h

sql/sql_audit.h

@@ -18,6 +18,7 @@
 
 
 #include <mysql/plugin_audit.h>
+#include "sql_class.h"
 
 extern unsigned long mysql_global_audit_mask[];