Removed obsolete code.
Iterate incoming intro-req twice.

This will ensure that even the first message in the batch will be
introduced to a candidate.
Unittests for candidates and walker.
Commentary changes.
Merge pull request #64 from boudewijn-tribler/unittest

More unit tests and small fix
Merge branch 'devel' of ssh://github.com/Tribler/dispersy into
probability_unitttests

Conflicts:
	tests/test_candidates.py