Implement 12-bit-specific error/warn/trace macros

The macros in jerror.h refer to j_common_ptr, so it is unfortunately
necessary to introduce a 12-bit-specific version of that header file
(j12error.h) with 12-bit specific ERREXIT*(), WARNMS*(), and
TRACEMS*() macros.  (The message table is still shared between 8-bit and
12-bit implementations.)

Fixes #607

jdatadst.c

@@ -21,7 +21,7 @@
 /* this is not a core library module, so it doesn't define JPEG_INTERNALS */
 #include "jinclude.h"
 #include "jpeglibint.h"
-#include "jerror.h"
+#include "jerrorint.h"
 
 
 /* Expanded data destination object for stdio output */