First handle the Transaction, then the deserialized decls: handling the transaction might trigger further deserialization (but no new transaction).
Fixed UInt_t for some of the tests where handling the first dummy TU transaction triggered deserialization, but deserialized decls were already handled.

Simplify isCanonicalDecl().


git-svn-id: https://root.cern.ch/svn/root/branches/dev/root6-pch@48927 27541ba8-7e3a-0410-8455-c3a389f83636