Fixed reporting of initial line during debugging.
Simplified lua interpreter launch/debug command.
Upgraded Mobdebug (v0.525) for performance improvements (also closes #121).

Other changes in the same version:
  Added handling of case-insensitive filenames on OSX.
  Improved debugging performance.
  Fixed terminating debugging of an empty script.
  Fixed resetting cached source as it may change when basedir changes.
  Replaced socket.select with non-blocking .receive as it is faster.