Add all=1 query param for atom feeds

Displays all items from all branches in one feed

Signed-off-by: Aaron Griffin <agriffin@datalogics.com>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -250,6 +250,8 @@ static void querystring_cb(const char *name, const char *value)
 		ctx.qry.period = xstrdup(value);
 	} else if (!strcmp(name, "ss")) {
 		ctx.qry.ssdiff = atoi(value);
+	} else if (!strcmp(name, "all")) {
+		ctx.qry.show_all = atoi(value);
 	}
 }