Make the fast walker more agressive:
     * Walk towards the trackers at each iteration.
     * Walk towards at most 10 newly discovered peers (before it was half of the
     newly discovered peers which was usually way less than 10)
     * Do at most 30 iterations (before it was 10)
Remove obsolete TODO entry
Merge pull request #376 from whirm/fix_fast_walker

Fix fast walker
Convert the fast walker loop to a LoopingCall
Merge pull request #377 from whirm/fix_fast_walker

Convert the fast walker loop to a LoopingCall
Fix copy-paste typo
Merge pull request #378 from whirm/fix_fast_walker

Fix copy-paste typo