Edited Feature: http_client - validate servers with custom certificates [116]

On non-windows platforms, openssl expects all valid certificates to reside in a directory like "/usr/local/etc/openssl". This can be problematic if the user program doesn't have root access, or the user doesn't want to permanently trust the certificate.

Proposed by eskech: [discussion](https://casablanca.codeplex.com/discussions/545078).