Boolean checks for all Dispersy.start() phases.
MainThreadCallback.start should just return True.
set _socket in constructor.
Fixes tool/tracker.py and tool/main.py
Code cleanup.
Removed obsolete code.
Cleaner start.
Changed MTU size warning into a debug message.
Unit test for tracker.py
Merge pull request #131 from boudewijn-tribler/private-search

Bug with starting Dispersy and code cleanups.