hide Proxy-Authorization just like Authorization is hidden

Submitted by:	Alvaro Martinez Echevarria <alvaro@lander.es>
Reviewed by:	Martin Kraemer, Ian Kluft, Dean Gaudet


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80295 13f79535-47bb-0310-9956-ffa450edef68