Change error reporting from exceptional.io to a SquareSquash instance at bugs.mcedit.net.

Exceptional.io is nice, but it is not appropriate for versioned desktop apps because it is designed for web apps where the latest version is the only deployed version.
Fixed: parentDir was an empty string when running from source.

Use abspath to avoid getting an empty string for the folder containing the script, when not frozen.
Submodule pymclevel updated.

Submodule pymclevel:
    > 2e43477 - Fixed: Biomes is a byte array, not an int array.
Setup: Add git commit ID to built apps in the GIT-COMMIT file.

Change release.py to find this file and RELEASE-VERSION inside dataDir
Debug: Remove dataDir from filenames in tracebacks, for crashes repoted from source checkouts.
Fixed: Missing graphics when running from a different working directory.

Open terrain.png and several other files from their location in dataDir instead of from the current directory.
Debug: Reverse error traceback and put the last callee first, similar to Java and Obj-C tracebacks.
Debug: Change pyo and pyc to py when reporting errors.