- Based on bug report #2498665 (http://curl.haxx.se/bug/view.cgi?id=2498665)

  by Daniel Black, I've now added magic to the configure script that makes it
  use pkg-config to detect gnutls details as well if the existing method
  (using libgnutls-config) fails. While doing this, I cleaned up and unified
  the pkg-config usage when detecting openssl and nss as well.