Correct the behavior and interaction between SSLProxyCheckPeer[CN|Name],

Correct the behavior and interaction between SSLProxyCheckPeer[CN|Name],
such that disabling either disables both, and that enabling either will
trigger the more comprehensive SSLProxyCheckPeerName behavior.

Only a single configuration remains to enable the legacy behavior, which
is to explicitly disable SSLProxyCheckPeerName and enable SSLProxyCheckPeerCN.

Major refactoring leads us to an alternate implementation for 2.4.21;
https://github.com/wrowe/patches/blob/master/fix_proxy_check_peer-2.4.x.patch

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1746645 13f79535-47bb-0310-9956-ffa450edef68