Check return codes after Popen() calls in fast_forward()

It is possible that one of these executions of Popen() will fail for one
reason or another.  Especially when certain Git functionality is not
available due to version differences.  Hence, the criticality of
checking the return code and raising an exception when it is non-zero.
Fix snoopys-sandbox-2 links
Fix integration test command example
Pass quiet option to git clone at sandbox initial cloning
Use communicate() rather than wait()
Merge remote-tracking branch 'sbesson/pipe_overflow' into error-handling
Allow passing of `--test-no-capture` / `-c` to setup.py

In order that we might mirror the `--capture=no` / `-s` functionality of
PyTest which is currently shaded by the use of `-s` to specify the
"suite" this command line option is added in this commit.
Add logging at ERROR after GitHubRepository.get_pull() exceptions

Without some form of logging at this or some other level in the stack
the sum total of information available following a failure to get access
to pull request metadata is:

    UnknownObjectException: 404 {u'documentation_url': u'https://developer.github.com/v3', u'message': u'Not Found'}

This is needless to say, insufficent.  Logging of failures will now
happen in the form:

    Failure to get pull request openmicroscopy/snoopys-sandbox#-1

With these changes it should be possible to debug missing repositories
or repositories for which the current user does not have access
permissions much more easily.
Add additional test case for a known pull request
Use same leading whitespace as other tests
Pipetastic `PIPE` avoidance and closure

This commit removes the use of `PIPE` where it is not required (replacing
it with `STDOUT` and/or `STDERR` redirection to `/dev/null`).  It also
performs various `Popen.wait()` return code checks using a combination of
`Popen.communicate()` and the `Popen.returncode` property.
Properly clean up after logging wrappers
Use cross platform null device
Merge pull request #162 from chris-allan/error-handling

Error handling, test expansion and general fixes