Add a test to ensure "apitrace trim" performs proper dependency checking

Here we trim a trace by specifying (with --calls) only the final
glXSwapBuffers and then test that we can still produce a matching
image from the trace. This will only succeed if "apitrace trim"
performs dependency checking and includes many previous calls.

Of course, historically "apitrace trim" performed no such dependency
checks, so older versions of apitrace are expected to fail this test.