Fix oversights

Missing test coverage for `frame_no` and `process_func` let in some API inconsistencies and some functionality missing from some classes.

This adds tests and makes several important (but I think uncontroversial) fixes.
Ok. Going forward, the tests will enforce it. Is your Tiffle-based class
ready to be tested added to api.py?

On Tuesday, June 24, 2014, Thomas A Caswell <notifications@github.com>
wrote:

> In pims/tiff_stack.py:
>
> > @@ -59,7 +59,7 @@ def class_exts(cls):
> >          return {'tif', 'tiff',
> >                  'stk'} | super(TiffStack_tifffile, cls).class_exts()
> >
> > -    def __init__(self, filename, dtype=None):
> > +    def __init__(self, filename, process_func=None, dtype=None):
> >          self._filename = filename
>
> My understanding is that ABC can only enforce mandatory class members
> (methods or properties), not the names/order of args/kwargs.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/soft-matter/pims/pull/52/files#r14148177>.
>