hg: build-infra/jdk8: Keep previous build.log as build.log.old when starting a new build.

[magnus.ihse.bursie at oracle.com]

Changeset: cd93c4248961
Author:    ihse
Date:      2012-06-11 15:02 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk8/rev/cd93c4248961

Keep previous build.log as build.log.old when starting a new build.

! common/autoconf/configure.ac
! common/autoconf/generated-configure.sh
! common/autoconf/spec.gmk.in
! common/makefiles/Makefile