[PATCH] Initial AIX portability fixes.

Added an AIX clause in the Makefile; that clause likely
will be wrong for any AIX pre-5.2, but I can only test
on 5.3.  mailinfo.c was missing the compat header file,
and convert-objects.c needs to define a specific
_XOPEN_SOURCE as well as _XOPEN_SOURCE_EXTENDED.

Signed-off-by: E. Jason Riedy <ejr@cs.berkeley.edu>
Signed-off-by: Junio C Hamano <junkio@cox.net>

mailinfo.c

@@ -8,6 +8,7 @@
 #include <string.h>
 #include <ctype.h>
 #include <iconv.h>
+#include "git-compat-util.h"
 #include "cache.h"
 
 static FILE *cmitmsg, *patchfile;