Use temporary binding for memory access base of bounds cast expressions

[kkjeer]

In checking for memory access violations for a bounds cast expression bounds_cast(e), use a temporary binding of e for the access base. This fixes a regression in memory access detection introduced in #694 (described in #695).

Testing:

• Re-enabled temporarily disabled out-of-bounds warning in checkedc/391.
• Passed local testing on Windows.
• Passed automated testing on Windows and Linux.

[dtarditi]

Looks good! Thanks.