databases/gnats4: Fix build failure on FreeBSD 10

gnats/gnats.h contains its own prototypes of asprintf() and vasprintf()
which conflict with the system ones:

In file included from edit.c:21:
./gnats.h:140:12: error: conflicting types for 'asprintf'
extern int asprintf (char **buf, const char *fmt, ...);
          ^
/usr/include/stdio.h:396:6: note: previous declaration is here
int      asprintf(char **, const char *, ...) __printflike(2, 3);

Just remove the prototypes from gnats.h.

Reported by:    miwi@

databases/gnats4/files/patch-gnats__gnats.h

@@ -0,0 +1,12 @@
+--- gnats/gnats.h.orig	2013-06-10 10:33:17.000000000 +0300
++++ gnats/gnats.h	2013-06-10 10:33:26.000000000 +0300
+@@ -137,9 +137,6 @@
+ # define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
+ #endif
+ 
+-extern int asprintf (char **buf, const char *fmt, ...);
+-extern int vasprintf (char **buf, const char *fmt, va_list args);
+-
+ #if ! HAVE_DECL_UNSETENV
+ extern void unsetenv (const char *name);
+ #endif