Fix for Bug #20246 (enum mysql_enum_shutdown_level not well-defined in mysql_com.h)

MYSQL_VERSION_ID is tested before it has been defined.  This leads to
a warning when compiling with -Wundef and it also will break the
internal logic of mysql_com.h as soon as MYSQL_VERSION_ID exceeds
50000.

The fix entailed a simple re-ordering of included files in mysql.h

include/mysql.h

@@ -65,9 +65,9 @@ typedef int my_socket;
 #endif /* my_socket_defined */
 #endif /* _global_h */
 
+#include "mysql_version.h"
 #include "mysql_com.h"
 #include "mysql_time.h"
-#include "mysql_version.h"
 #include "typelib.h"
 
 #include "my_list.h" /* for LISTs used in 'MYSQL' and 'MYSQL_STMT' */