Use ap_bin2hex instead of sprintf(..., "%02x". It gives the same output and is faster.

No real speedup should be achieved on production machine, because this is done
only for characters that need to be escaped. 
However, this will close PR 50919.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1429564 13f79535-47bb-0310-9956-ffa450edef68