@safe'ty of find and canFind

Change find's tests to validate usability of @safe.
Eliminate the trustedFindRR case by pushing it down a layer in the find stack of functions.
Mark unpredictableSeed as @trusted (@safe is a stretch due to all the casting) so that it can be used in @safe contexts.
Mark canFind's tests to validate usability of @safe (which lead to the unpredictableSeed change)
Works for me, I was just bringing it up since I still remembered it. I think it makes sense that it be useable in safe code. @WebDrake : Are you opposed to this here?