Add Verisign G5 CA cert and its intermediary

https://s3.amazonaws.com changed its certificate.  We did not have the
new root CA certificate (the G5 certificate) in our default certificate
list.

This caused connections to https://rubygems.org to fail for users who
did not have a full certificate list for openssl installed separately.

Now we have both the G5 certificate and its intermediary to allow
connections to succeed for users on cert.pem-less systems.

Fixes #665

Fixes #671
Remove redundent certs
Add #654 to history

Issue #654 removed redundant (useless) certificates that aren't needed
to connect to https://rubygems.org.  This was committed in @22e5981.

Fixes #654