Initial attempt to catch exceptions based on their type.
Enable try/except within functions.

User local $err instead of $loc.err to hold thrown object.
Cleanup except code a bit.
Make raise on it's own re-raise current exception.
Comments about where finally needs to execute.
Fix missing or incorrect exception calls and update test cases to match.
Rebuild dist.

All tests pass.
Rebuild regentests.
Merge pull request #91 from rixner/master

More complete implementation of try/except