Fix widget install and uninstall
Use hardlinks for widgets.
XBMC Update from 12.2 to 12.3

Updating cask to pull latest version of XBMC (12.3).
Distinguish between checking SHA-1 & SHA-256 sums

A couple casks use SHA-256 checksums. Add language to describe how to
determine those checksums in an easy way.
fix test cruft introduced by #2304