Debug Info: Remove unused code. The MInsn of an _abstract_ variable is
never used again and updating the abstract variable for each inlined
instance of it was questionable in the first place.
Fix some minor typos in tests
Make runlines consistent with other dll attribute tests
[ADT] Delete the Twine assignment operator

This makes it slightly harder to misuse Twines.  It is still possible to
refer to destroyed temporaries with the regular constructors, though.

Patch by Marco Alesiani!