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.
Ditto on this case. The shared args should be consistent between classes.
Leaving it inconsistent is worse than changing the API of relatively young
code.

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
>
> ditto on adding kwargs not at the end.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/soft-matter/pims/pull/52/files#r14129912>.
>