moving SSLVerifyClient directive parsing into ssl_cmd_verify_parse

function, which can also be used for SSLProxyVerify directive.

dropping support for undocumented integer form of levels (0..3)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/ssl@93870 13f79535-47bb-0310-9956-ffa450edef68