Fix handling of directories of builds

Add delete_builds.pl - a utility for making space quickly on build machines This Perl script deletes some directories known to contain very large files first, before deleting the rest of the build which contains millions of small files. Given multiple builds, it will do this breadth first, so that lost of space is released quickly.

v0.20 - change to developer-secure.symbian.org, to fix Bug 3627 Also move the point at which downloadpage.html is saved, in order to get all of it for debugging