Merge r425210 from trunk:

* Add a check to make sure that the base provider and the alias names are
  different and also that the alias has not been registered before.

PR: 40051
Submitted by: bnicholes
Reviewed by: bnicholes, rpluem, fielding


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@425740 13f79535-47bb-0310-9956-ffa450edef68