Various Brainware IO class cleanups.

This pull request fixes various issues with BrainwareSrcIO, BrainwareF32IO, and BrainwareDamIO, including issue #146 and the issue raised with the timing of the Events.  It also ports BrainwareSrcIO to use EventArray instead of Event.

There are also another couple minor fixes.  First, SpikeTrain now properly copies the lazy_shape attribute if present.  This should be included in all array types when ported.  It also splits the path handling on iotest/tools.py into its own function so it can be used separately.