minor lvchange option validation refactor

Hi,

I would normally check this in right away, but on a second thought (since I got the change wrong the first time), an extra reading of the patch can't hurt (just check with good old De Morgan's). It is passing testsuite (now).

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Thanks!
Petr.

PS: I ran into this sorting through stale mail. I may have a few more such outlandish ideas as I sort through more of it.

Ack. Read it through, looks like a good refactor that clarifies the code.