Changes in FindPetsc and related modules from Flow123d#3

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jbrezmorf wants to merge 9 commits intojedbrown:masterfrom

jbrezmorf:master

Commits on Sep 4, 2013

Commits on Sep 5, 2013

Make minimize changes compared to Jed's version.
jbrezmorf
committed

Commits on Sep 6, 2013

Commits on Oct 2, 2015