Removes MemberDestination.

Using MemberDestination can result in messages not being delivered
when the walker did not recently visit the member in question.  Using
CandidateDestination is preferred.

Currently only the signature request uses MemberDestination, we have
rewritten it to use CandidateDestination instead.  Since neither of
these destinations add anything to the binary packet, this change is
fully backwards compatible.
Fixes issues with signature request.
Merge remote-tracking branch 'remotes/upstream/devel' into livebartercast

Conflicts:
	dispersy.py
Merge pull request #87 from boudewijn-tribler/livebartercast

Removes MemberDestination.
Adds unit tests for double signed signature requests.
Adds new sign=True parameter.
Merge pull request #88 from boudewijn-tribler/livebartercast

Most of this is beyond my comprehension of Dispersy, but if it works it works.
Enable or disable bloom filter sync.

When dispersy_enable_bloom_filter_sync is False:
- dispersy_take_step will always be called with allow_sync = False
- acceptable_global_time will return 2 ** 63 - 1 instead of its
  previous calculation involving current global time, mean
  neighborhood global time, and dispersy_acceptable_global_time_range.
Merge pull request #89 from boudewijn-tribler/enable-sync

Enable or disable bloom filter sync.
Update test_overlay.py

This test is run daily on Jenkins and always fails because there are not sufficient people running the barter community yet.