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/partition_element.h

@@ -16,6 +16,9 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA */
 
+#include "my_base.h"                            /* ha_rows */
+#include "handler.h"                            /* UNDEF_NODEGROUP */
+
 /**
  * An enum and a struct to handle partitioning and subpartitioning.
  */