ECPG threads test

Hi!

From what I can see, the ecpg thread tests (src/interfaces/ecpg/threads)
don't ever run. They rely on ENABLE_THREAD_SAFETY to be set, but even when
I build with --enable-thread-safety, it's not set. This is because ecpg
does not pull in pg_config.h, and also does not specify it on the
commandline.

Or am I missing something completely here? FWIW, it's not running the
threads test on windows or linux in my tests, but I may have missed
something...

//Magnus