Provide a generic (template) operator!=.
Provide NowTransition.Location() method.
Create NOW instrumentation on reaching assertion.

Rather than creating *all* instrumentation functions for NOW events in *every* instrumented file (oops!), just create each function on-demand when we reach the assertion site.

We don't need to worry about other instrumentation passes coming along and modifying it later, because there is only one NOW event per assertion site.