RFR: JDK-8035495 Improvements in autoconf integration

Fri Feb 21 13:31:40 UTC 2014

This bug covers several small improvements in how our configure 
eco-system integrates with autoconf. More specifically:

* Fix so config.status --recheck works.
* Let the top-level configure script determine TOPDIR, and pass it on.
* Clean up usage regarding TOPDIR, SRC_ROOT and AUTOCONF_DIR.
* Prohibit direct execution of common/autoconf/configure; always use 
configure in top-level dir.
* Add "do not edit" header to generated-configure.sh
* Add output on how we determine where to store the configuration.
* Improve output from autogen.sh, including autoconf version.
* Unify duplicated code in autogen.sh

Bug: https://bugs.openjdk.java.net/browse/JDK-8035495
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8035495-improvements-in-autoconf-integration/webrev.02

/Magnus