Remove tools/git2svn.pl

We no longer mirror out Git repositories into Subversion.
tools: Remove Drupal/SourceForge scripts

We moved our web site away from Drupal and the snapshots/guidelines away
from SourceForge.  The new infrastructure scripts will be maintained in
a separate repository together with the Markdown source of the new web
site.
Add tools/generate-change-log

Add the tools/generate-change-log script for auto-generating the
ChangeLog file from the Git history when running "make dist".