Feature tests for bounds-safe interface implicit type conversions. (checkedc#59)

This change adds feature tests for implicit type conversions at bounds-safe interfaces.   It includes three sets of tests, corresponding to each language construct that can have a bounds-safe interface: a set for parameters with bounds-safe interfaces, a set for non-locally scoped variables with bounds-safe interfaces, and a set for members with bounds-safe interfaces.  These tests match corresponding compiler changes for Checked C clang repo issue 31.

For each set of tests, there are
- tests for assigning (or passing) checked pointers to unchecked pointers with bounds-safe interfaces (where the referent types match)
- tests for assigning or passing checked pointers to void * pointers with bounds-safe interfaces
- tests for passing checked void pointers to non void * pointers with bounds-safe interfaces.  These tests are expected to cause errors.
- There are also tests for types involving type qualifiers, making sure that the qualifier restrictions are enforced (a pointer to  non-const type can be assigned to a pointer to a const-type, but not the reverse).

There are additional tests for parameters with array types.  During type checking, the array types are adjusted to be pointer types.  For Checked C, the bounds-safe interface types are checked array types and they are adjusted during type checking to be checked pointer types.    For multi-dimensional arrays, this ends up being a little subtle.  The multi-dimensional array has a bounds-safe interface type that is a checked multi-dimensional array.   The checkedness propagates to the nested array types.  
When the checked multi-dimensional array type is adjusted to be a pointer, the result is a "checked pointer to a checked array type."

There are tests for both 1-dimensional and 2-dimensional array parameters.  The 2-dimensional array parameter tests check the subtleties of multi-dimensional arrays.  Each multi-dimensional argument is typed as a "checked pointer to a checked array type", so if the appropriate adjustments did not happen for the bounds-safe interface type for the parameter, a type mismatch would occur.

Author: dtarditi