@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)
Yeah. Segfaults are perfectly memory safe. The only risk is if the object type is large enough, then you don't get a segfault (I don't remember the details though - something having to do with pagesize I think, but an object had to be _ridiculously_ large for it to happen), but that wouldn't be the case here. And there was some discussion of adding null pointer checks for those rare cases, in which case, dereferencing null would be safe in even those cases.