treewide: be explicit about dependence on gettext.h

Dozens of files made use of gettext functions, without explicitly
including gettext.h.  This made it more difficult to find which files
could remove a dependence on cache.h.  Make C files explicitly include
gettext.h if they are using it.

However, while compat/fsmonitor/fsm-ipc-darwin.c should also gain an
include of gettext.h, it was left out to avoid conflicting with an
in-flight topic.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/parse-options.c b/parse-options.c
index 6dd4c09..084b4f1 100644
--- a/parse-options.c
+++ b/parse-options.c
@@ -4,6 +4,7 @@
 #include "config.h"
 #include "commit.h"
 #include "color.h"
+#include "gettext.h"
 #include "utf8.h"
 
 static int disallow_abbreviated_options;