disable VC for batch evaluation

* mk/default.mk: Disable VC during batch evaluation.

This speeds up file handling, especially on Windows where Git can be
very slow.

mk/default.mk

@@ -65,7 +65,8 @@ BTEST	= $(BATCH) \
 
 # Using emacs in batch mode.
 # BATCH = $(EMACS) -batch -vanilla # XEmacs
-BATCH	= $(EMACS) -batch -Q
+BATCH	= $(EMACS) -batch -Q \
+	  --eval '(setq vc-handled-backends nil)'
 
 # Emacs must be started in toplevel directory
 BATCHO	= $(BATCH) \