Disable SSLv2, to fix new/from-ports OpenSSL builds.

Newer and ports-based builds define the SSLv2_client_method() in the
headers unless OPENSSL_NO_SSL2, or, depending on version,
OPENSSL_NO_SSL2_METHOD is defined, however newer OpenSSL versions in
FreeBSD no longer provide the implementation in the library.

Preload the autoconf (configure) cache to pretend SSLv2_client_method()
were universally _un_available, effectively disabling SSLv2 altogether.

PR: 209596
Submitted by: peter@ [first proposal], mandree@ [committed proposal]
Reported by: peter@
Approved by: chalpin@cs.wisc.edu (maintainer)