Fix #299 by demoting filter errors to 'debug'

Also log more about where a failling filter came from
Log error type name too
Test #299 fix
Remove inert test

This test wasn't doing anything: _filter would error since it's looking
for f['filter'], not f['callable'], rather than the thing we were
testing for.

Incidentally, this test would fail if it worked: does LoadableManager
need modifying?
Refactor exception type logging
If filter errors are all caught by _filter, needn't catch them here too
Merge remote-tracking branch 'daniel/fix-299-filter-errors' into develop

Conflicts:
	habitat/parser.py