Merge 'warnfree' into 'trunk'

Merge 'warnfree' into 'trunk'

Another round of warning-squashing:
Fix source registration/unregistration in several places
Accomodate postgres being really load on CREATE
Move the taint tests to a non-mainstream schema - hopefully this one will not be disturbed for a while
Fix warning due to File::Copy being sloppy
Test for TxnScopeGuard warnings
Test for multiple register_class warnings
Blindly silence a weird warning within a TODO in t/47bind_attribute.t. Hopefully when the TODO is resolved, it will be obvious what was causing it