Have pfsinstall allow re-installing versions, but with new dependencies.

We sometimes need to install a (git) version of a product again, after having only updated some of the product's dependencies. We obviously want to do this without modifying the existing installed version. We have been doing this by hand, sorry to say.

This change will do that: if you run, say, `pfsinstall tron_actorcore:2.4.11` and that version has already been installed, a new version will be installed with the eups tag `2.4.11a` (or b,c,d, etc). As always, the new installation will pick up the current or setup versions of all dependencies.

The mechanism is merely to arrange to calculate and pass `VERSION_SUFFIX` to the `eupspkg install/decl` calls. The LSST machinery to do so is a bit more elaborate that we want to buy into, and now seems to want to use SHAs in ways I do not understand.