Tidy up ro.cm.version (needed to support 3 year old sdcard installer)

There are tens of thousands of copies of that sdcard script floating around for these three-year old devices.
People are not going to think about this hard enough to want to upgrade their installer script. I don't have a choice, really.

Change-Id: Iba8f5ee2f8f8b5ba7854c92a2990ca1dc3ad88d7