Merge r1583175 and r1593745 from trunk:

mod_alias: Stop setting CONTEXT_PREFIX and CONTEXT_DOCUMENT environment
variables as a result of AliasMatch.

Submitted by: covener
Reviewed by: jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1594539 13f79535-47bb-0310-9956-ffa450edef68