updated entity checker

["Wichmann, Mats D" <mats.d.wichmann@intel.com>]

The latest entity checker now has the option
of checking md5 sums against a saved checklist
(I added one as extras/md5sums), or to generate such
a checklist if asked to.  Only "found" entities -
listed in the package file and also in the
package or patch directory - participate in
the checksumming, which is off by default.
The logic should hopefully be right now for
both split package and patch directories
(as in the app battery) and combined (as in
the LSB-si), so the same tool can be shared.

Mostly I just wanted to have some fun,
and this bit of Python hacking was more fun 
than I've been having recently, so there (grin)

Mats