-some python2.5 compatibility
-moved platform_py to system.py, turned into singleton
-added shell detection to system.py
-improved on existing shell detection via psutil module, this is also x-platform
-added settings API
-removed some settings from configure/install.sh, now handled at runtime by settings singleton instead
-fixed rez-dot so you can change img format; changed default from jpg to png,
 jpg has issues on old centOS distros;
-added rezconfig file, part of new settings system
-ported Rex to use system.py
-removed some now unused settings from configure.sh