hg: build-infra/jdk8: Improved usability for handling multiple configurations:

[magnus.ihse.bursie at oracle.com]

Changeset: 3b6da71de932
Author:    ihse
Date:      2012-05-03 10:35 +0200
URL:       http://hg.openjdk.java.net/build-infra/jdk8/rev/3b6da71de932

Improved usability for handling multiple configurations:
* User can select one or many configurations using CONF=<configuration name substring>.
* User can select all configurations using CONF=.
* Old-style SPEC= selection can still be used.
* User can build any top-level make target for selected configurations.
* Name of configuration is printed when building.
* Incorrect usage will give explicit help about what's wrong.

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