Flush stdout

As noted in email, it seems that failing to flush stdout in the sub-processes means that some output might go missing. I've observed this in practice with Syntastic in Vim. Here I flush both stdout and stderr before sending the message back to the main process that will allow it to continue. This makes the problem disappear for me.

It occurs to me that if sub-processes are producing output independently, there is also be a risk that they will badly interleave their output. I haven't looked into this - my primary concern is invocation for a single file at a time.

See merge request !7

Subprocesses write to stdout. They must flush their output before the
main process exits to avoid losing output or confusing the calling
program.

make flake8 pass in dirty flake8 root directory

See merge request !6

Add exclude list to tox.ini

Add usedevelop to tox.ini

See merge request !5

I have seen people who place the comment at the bottom of the file and it
would be backwards incompatible if we did anything but preserve it as a search
instead of match

Only match '\s*# flake8[:=]\s*nqa' when it happens at the beginning of a
line. The previous version of this regex is incorrectly hitting the
following line:

        # Any "# flake8: noqa" line?

Causing flake8 to not be run on engine.py.
Also fix flake8 issues in engine.py.

Add a .gitignore file

See merge request !3

Tox 1.6 has a feature to install code into the virtualenv via 'setup.py
develop' This makes it easier to source the tox virtualenv and test code
changes.