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_sort.h

@@ -16,6 +16,18 @@
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */
 
+#include "my_global.h"                          /* uchar */
+#include "my_base.h"                            /* ha_rows */
+#include "my_sys.h"                             /* qsort2_cmp */
+
+typedef struct st_buffpek BUFFPEK;
+typedef struct st_queue QUEUE;
+typedef struct st_sort_field SORT_FIELD;
+
+class Field;
+struct TABLE;
+
+
 /* Defines used by filesort and uniques */
 
 #define MERGEBUFF		7