Python3 compatibility fixes

- Add Python3 compatibility wrapper from imp.find_module
- Python3 does not have a long type
Automatic Unicode decoding for python3 plugins

- In Vim :py3 returns unicode strings to the caller, for compatibility
  automatic decoding is now enabled for plugins in python3
Merge pull request #50 from equalsraf/tb-python3-fixes

python3 fixes for find_module, long, unicode