Bug: Version checking is no longer working correctly

Description:

Version checking is no longer working correctly. There are multiple problems:

• A .srcfiles.yaml file requiring a higher version does not generate any warning when a lower version is used. E.g., specify 1.7.4 in .srcfiles.yaml and version 1.7.3 won't complain (it should).
• Specifying an option that requires a specific version does not warn if the current ttBld version is too low to handle it.

These are both regressions -- so we need to make certain these are fixed in a way that will make it less likely to break it in the future.