Add cgit_for_each_namespaced_ref_in helper

libgit has a for_each_namespaced_ref,
but lacks equivalents for just branches, tags or remotes.

Rather than implementing all of those helpers,
it's more convenient to implement just one
that prepends the namespace to the provided ref base.

Signed-off-by: Richard Maw <richard.maw@gmail.com>

cgit.h

@@ -394,4 +394,6 @@ extern char *get_mimetype_for_filename(const char *filename);
 
 extern int cgit_get_sha1(const char *name, unsigned char *sha1);
 
+extern int cgit_for_each_namespaced_ref_in(const char *prefix, each_ref_fn fn, void *cb_data);
+
 #endif /* CGIT_H */

shared.c

@@ -651,3 +651,13 @@ int cgit_get_sha1(const char *name, unsigned char *sha1)
 		return get_sha1(name, sha1);
 	}
 }
+
+int cgit_for_each_namespaced_ref_in(const char *prefix, each_ref_fn fn, void *cb_data)
+{
+	struct strbuf strbuf = STRBUF_INIT;
+	int ret;
+	strbuf_addf(&strbuf, "%s%s", get_git_namespace(), prefix);
+	ret = for_each_ref_in(strbuf.buf, fn, cb_data);
+	strbuf_release(&strbuf);
+	return ret;
+}