More work on version checking.

1. Now check for minimum rbtools as well as ptyhon.
2. Use constant variables for the versions instead of hard-coding.
More 2.4 compatibility gyrations.

1. Improved the version message to warn users about updating python.

2. Replaced the wonderful 'with' statements with the awful nested 'try'
   statements to prevent syntax errors for those running on 2.4.