Enable wt-status output to a given FILE pointer.

Still defaults to stdout, but you can now override wt_status.fp after
calling wt_status_prepare().

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wt-status.h

@@ -1,6 +1,8 @@
 #ifndef STATUS_H
 #define STATUS_H
 
+#include <stdio.h>
+
 enum color_wt_status {
 	WT_STATUS_HEADER,
 	WT_STATUS_UPDATED,
@@ -19,6 +21,7 @@ struct wt_status {
 	int commitable;
 	int workdir_dirty;
 	int workdir_untracked;
+	FILE *fp;
 };
 
 int git_status_config(const char *var, const char *value);