Append date to checkout log (don't overwrite it).

client.mk

@@ -167,7 +167,7 @@ checkout:
 	@date | tee $(CVSCO_LOGFILE)
 	cd $(ROOTDIR) && \
 	  $(CVSCO) $(MOZ_CO_MODULE) 2>&1 | tee -a $(CVSCO_LOGFILE)
-	@date | tee $(CVSCO_LOGFILE)
+	@date | tee -a $(CVSCO_LOGFILE)
 	@conflicts=`egrep "^C " $(CVSCO_LOGFILE)` ;\
 	if test "$$conflicts" ; then \
 	  echo "$(MAKE): *** Conflicts during checkout." ;\