fix https_proxy problem for IO::Socket::SSL and Net::SSL, includes extensive test (Part#1)

Hi,
this change fixes the behavior of https_proxy.
Current behavior: send unencrypted requests with https:// URLs to specified proxy
Correct behavior: create encrypted tunnel to proxy and send requests within
This is part#1 of the change, the rest is in lwp-protocol-https

Regards,
Steffen Ullrich (maintainer IO::Socket::SSL)