Unclear error when ig.Graph.Read() given bad file path

[nickeubank]

In python 3.4, when one uses ig.Read.Graph('file', format='pickle') and passes a bad file name (with a typo or something), the error is very hard to understand -- the error is:

TypeError: 'str' does not support the buffer interface"

The error occurs at line ~1801 of init.py at the line result = pickle.loads(fname)

I've offered one solution in PR #41

[ntamas]

#41 is merged now so I'll close this.