Make TrimToPrefix /slightly/ more efficient

Also test for the incredibly unlikely corner-case where the date
pattern is used in the prefix.
Test for a few more corner-cases
bash completion support

Should be fairly full-featured.

Supports one of the shells listed in Issue #51.
Move periodic scripts to their own folder

Remove capitalization from zfSnap
Update periodic scripts -- untested

I don't have access to a FreeBSD box yet, so this is untested.

The majority of changes are whitespace (tabs to spaces) and comments
fixes.

The only real functional change was to update the `zfsnap` calls to the
new syntax.