Updates and local hacks for iiglue implicit dependencies.

All iiglue output implicitly depends on z3.  Also, add some hacks for
implicit dependencies created or affected by our special iiglue wrapper
script, if that script is indeed being used.

These changes make scons smarter about when iiglue output should be
rebuilt for regression tests.  For example, if we rebuild iiglue
itself or install a new version of z3, scons now knows that all
iiglue-created JSON files should be rebuilt.