Correct SSLProxyMachineCertificatePath and SSLProxyMachineCertificateFile -

the previous description looked like it was copied from SSLProxyCA*
Also add a warning about not using encrypted keys in those two.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@102191 13f79535-47bb-0310-9956-ffa450edef68