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
More candidate/walker related counters.
Output debug statistics when logger is enabled.
Merge remote-tracking branch 'remotes/upstream/devel' into bugfixes
Spellcheck.