Added support for building under Linuxbrew (a linuxbrew version of MacOS Homebrew)
Patch from Matthew Altus, that implements SSL_CTX_set_psk_client_callback() and SSL_set_psk_client_callback().
Patch to build with LibreSSL has no support for NPN
Also skip the NPN test if the SSL library is LibreSSL.
Fixed a problem with a variable declaration in ssleay_session_secret_cb_invoke reported by Graham Ollis.
Significant patch set from Open System Consultants:

• Bugfix: tlsext_status_cb_invoke(...): free ocsp_response only when allocated.