mjo-proof_by_cases.tex: indent the cases and use italics for "Case N".

mjo-proof_by_cases.tex: indent the cases and use italics for "Case N".

This is an aesthetic choice that will probably change every time I
write a paper that uses this environment. In my current endeavor, I
think having the cases indented is necessary to separate them from the
rest of the document (to show that they're still part of the current
theorem/proof). Moreover the use of italics keeps the reader from
lumping the "Case N" in with the stream of bold Definitions,
Propositions, Theorems, and Examples surrounding them.

I've checked that this change isn't fatal to either my thesis
(double-spaced) or my polyhedral positive operators paper.