TODO: Document a 'make check' problem I ran into

I had the bad luck to compile a connect-uri-nbds-certs that failed
100% of the time on my system, because $(RANDOM2) had picked a port
that was in use.  I fixed the failures by 'touch tests/connect-uri.c'
before 'make check', but didn't have time to make the fix more
permanent by linking in pick-a-port.c to choose the port dynamically.