apache2: Apache 2.4 support.

Apache 2.4 renames the conn_rec struct member name from "remote_ip" to
"client_ip". Detect 2.4 and use COSIGN_CLIENT_IP macro to use the correct
struct member name for 2.2 and 2.4.
Preliminary patch for SF.net request #13: allow custom friend DB name
Add missing #undef HAVE_APACHE_CONN_CLIENT_IP to config.h.in.
Fix compiling for Apache 2.4.x.
Disable SSLv2 in cosignd and cosign.cgi.

Unlikely it was ever used, since clients use SSLv23_method() when creating
the SSL context, negotiating to the highest option supported by the server.
Nevertheless, SSLv2 is like WEP: never to be used, anywhere, ever.
"make test" updates: bump key bits to 2048