Fixes various issues with shallow copying.

* The {.shallow.} pragma is now properly respected for objects and
  tuples that are not handled by genGenericAsgn(). Mirroring the
  decision in generic assignments, whether an assignment is shallow
  depends on the destination of the assignment, but not the source.
* String literals and complex inline constants are now properly assigned
  a location kind of locData.
* Assignments from a locData source will now force deep copying to
  occur, even if shallowCopy or {.shallow.} is being used. This
  avoids potential crashes from `shallowCopy s, "xxx"` or from
  `shallowCopy t, ("a", "b")`.
Merge pull request #691 from rbehrends/fix-shallow-pragma

Fixes shallow pragma for objects and tuples.