Make configuration file suffix configurable

As outlined in 5b530b5, this lets us have additional configuration files which can be given preference over ```.bioformats```.  So for dev_4_4 jobs, we can do something like:

```ant -Dtestng.directory=/path/to/repo -Dtestng.configSuffix=stable test-automated```

Then for each subdirectory, if a ```.bioformats.stable``` file is present, that will be used as the configuration file.  If ```.bioformats.stable``` is not present but ```.bioformats``` is, then ```.bioformats``` will still be used as before.  If ```testng.configSuffix``` is not set, it is assumed to be empty (i.e. ```.bioformats``` will be used across the board).

This is not quite ready for review yet, as it's being used to confirm that http://hudson.openmicroscopy.org.uk/view/All/job/BIOFORMATS-repo-stable-for-debugging/ will pass - there may be a few more small changes necessary to make that happen.  Once that job is passing, I'll copy the configuration to ```BIOFORMATS-full-repository-stable``` and delete it.

This was discussed briefly with @joshmoore and @sbesson.