Fix python 3 problem: 'str' does not support the buffer interface
Replace built-in hash function with hashlib.

The built-in hash function returns inconsistent values in Python 3.
Merge pull request #76 from 9m66p93w/hashing

Replace built-in hash function with hashlib.
Cosmetics
Remove useless comment
Update NEWS
Merge pull request #75 from davidaurelio/master

Fix python 3 problems with default rights
Simple try/except import trick
Return an int for __hash__
Store collection's parent in database (bug #77)
Fix sql schema
Fix schema again