phabricator: fix a phabsend crash when processing a renamed binary
This was a trivial fix, and some more tests are added to cover binary files.
Since the old filecontext is passed in, the old name is still available. But I
noticed some weirdness around what it marked as binary and not, and what is
viewable in Phabricator. Those things have been flagged, and will probably take
some digging.
Differential Revision: https://phab.mercurial-scm.org/D8133
Hello, Foobar
[b'Hello, Fo, =;:<o', b'Hello, Bar']