Deprecate WikiRevision::$fileIsTemp and fix $isTemp

Deprecate WikiRevision::$fileIsTemp and fix $isTemp

Cleanup from 43d5d3b682cc1733ad01a837d11af4a402d57e6a

This commit introduces both $fileIsTemp $isTemp
It would appear that the intent was to have one property here
and it looks like both of these are meant to do the same thing.

It also looks as if both public properties are actually unused
(only used by the getter and setters)

As isTemp will now sometimes return true line 766 $autoDeleteSource
will be true in new cases.
As a result $tmpFile->autocollect(); will be called in more cases

Change-Id: I8014172fb9fd7a0e4a89d0872bafdf6c50f92646