Improve workaround for OpenSSL 1.0.0k/1.0.1e

Extend and improve the workaround introduced in commit 20b3f66120.
Automatically replace SSL_get_certificate() with a drop-in replacement
if a version of OpenSSL known to be broken is used.  This now covers the
use of SSL_get_certificate() within the connection manager as well and
resolves one more case where OpenSSL could crash.