git_mkstemp_mode, xmkstemp_mode: variants of gitmkstemps with mode argument.

gitmkstemps emulates the behavior of mkstemps, which is usually used
to create files in a shared directory like /tmp/, hence, it creates
files with permission 0600.

Add git_mkstemps_mode() that allows us to specify the desired mode, and
make git_mkstemps() a wrapper that always uses 0600 to call it. Later we
will use git_mkstemps_mode() when creating pack files.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wrapper.c

@@ -204,6 +204,16 @@ int xmkstemp(char *template)
 	return fd;
 }
 
+int xmkstemp_mode(char *template, int mode)
+{
+	int fd;
+
+	fd = git_mkstemp_mode(template, mode);
+	if (fd < 0)
+		die_errno("Unable to create temporary file");
+	return fd;
+}
+
 /*
  * zlib wrappers to make sure we don't silently miss errors
  * at init time.