[Ocaml-lib-devel] Minor mods to xarray

[Brian H. <bh...@sp...>]

Kicked off by my discussion with John Max Skaller in this list.

- made the type of resizer functions a named type (cleaning up a lot
of code and type definitions)
- added a third parameter to the resize functions- the old length of
the array (tells them if we're inserting or deleting)
- named the arguments to the resizer functions so I can fargin remember
what order they go in.
- Added a conservative resizer function to demonstrate why I added the
oldlength parameter.
- Cleaned up and (hopefully) improved several comment, especially
about resizer functions.
- Cleaned up exponential_resizer, so hopefully it's clearer what it's
doing.  And it doesn't need to be recursive anymore.
- Allowed 0 length arrays in a lot more places.
- changed name of newlength to changelength, to stop some name collisions

Brian