github pull request #733 - prices of unID'd gems

Pull request from vultur-cadens:  don't change unID'd gem prices
when source changes insert some new object before them or the game
gets rebuilt with different featues enabled such as MAIL.

This is more about keeping the spoiler table in the wiki accurate
than anything to do with game play.  It definitely gives players
who use spoilers an advantage over ones who don't, but does so in
such an insignificant aspect of play that it likely doesn't matter.

I'm fairly sure that the remark that keeping the prices the same
is what the original implementor intended is not correct.  I don't
recall who implemented this and the commit log for the first cvs
repository is long gone so it's moot.

Fixes #733