It seems http2, x509 and tls errors are not pointer errors, after all.

I mostly found this through the fact that even after the last patches it
still didn't match them, but now there are finally tests for all of
them, so hopefully this will be a permanent fix.

This was dropped as part of #2008 but it will be better if we
differentiate between different timeouts

Also add test for the `request timeout` error code in `httpext`