[SAC] Buildbot accommodations

[Howard Butler]

All,

Mateusz and I added support for post-commit hooks for the GDAL  
subversion repository to push its changes to GDAL's buildbot.  This  
means that as changes are made, new builds are generated.  The  
following items on osgeo1 were added:

- Twisted Python to support the svn_buildbot.py hookscript
- svn_buildbot.py was added to /var/www/svn/hookscripts
- A new outbound firewall rule, /etc/sysconfig/iptables-custom/ 
BUILDBOT to allow outbound connections on 1500
- svn_buildbot.py was added as a post-commit hook to GDAL's repository  
in /var/www/svn/repos/gdal/hooks

The setup allows other buildbots for other repositories to be fired if  
they wish with the commit-hook by modifying their post-commit hook  
scripts and adding another outbound connection line to the BUILDBOT  
firewall rule.  If you notice any problems, or commits cannot complete  
for some reason, disable the hook script by commenting out the  
svn_buildbot.py script call in GDAL's post-commit hook.

Thanks for the hard work Mateusz!

Howard