Cache last_processed_block in config directory.
Improve a test.
Update to asyncio 0.4.1.
Improvements to Blockfetcher.py.
Merge branch 'changetip' into local_master

Conflicts:
	pycoinnet/helpers/tests/test_standards.py
	requirements.txt
Deal with different semantics of put_nowait.
Fix test_InvCollector_simple.
Revert "Deal with different semantics of put_nowait."

This reverts commit ca25fc721c50eef536919f3cb8023d6ca14819da.
Keep references to some tasks so they're not garbage-collected.
Get tests dealing with lists instead of tuples.
Improve InvColelctor test.
Fix tests.
Revert "Get tests dealing with lists instead of tuples."

This reverts commit 774f4de74549b6bb8a973b0bcfd5bd4b95ef25f0.
Fix InvCollector test.
Make sure ping & pong tests are not garbage-collected.
Be more careful about not garbage collecting tasks.
Use weakset in InvCollector.
More strong references to Task objects.
Update comment.
Remove asyncio dependency from BlockChain.py.