Added keyword argument, default_opts, to rsync_project.

Previously there was no way to remove any of the predefined rsync options. This
change allows them to be modified via a keyword argument.
Rebased off 1.7.0 and moved arg order.
Tweak changelog entry
Formatting tweaks
Docstring tweaks
WIP
Dumb consistency tweak
Allow integration tests to load mock_streams decorator
Merge branch 'master' into 910-int
Integration tests re: #910.

Turns out the mock_streams stuff wasn't strictly necessary.
Keeping it in anyway since it will be later.