Add memory checks on GetReceiveFolder mysql backend function
Initialize MessageClass prior call to openchangedb_get_ReceiveFolder
Fix small memory leak
Merge pull request #48 from openchange/jkerihuel/cr-2069

Add memory checks on GetReceiveFolder mysql backend function
Prevent mapistore_init() from overwriting mapping_path if it was
previously set with mapistore_set_mapping_path().
Add preliminary python-c gateway for OpenChange backends:
- Implement init() and create_context()
- Add a sample.py python backend
- Make backend testable through mapistore_test binary
Merge branch 'jkerihuel/mapistore-python' of https://github.com/openchange/openchange into jkerihuel/mapistore-python