of failing to check negative-wraparound of int32 operands.
- Add casts and XXX comments to MSG_* calls that lack prototypes.
- #ifdef XP_UNIX around MimeHeaders_do_unix_display_hook_hack.
git-svn-id: svn://10.0.0.236/trunk@13463 18797224-902f-48f8-a5cc-f745e15eee43