Merge r1618851 from trunk: mod_authz_core: Allow <AuthzProviderAlias>'es
to be seen from auth stanzas under virtual hosts. PR 56870.

Submitted by: covener
Reviewed/backported by: jkaluza


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1626207 13f79535-47bb-0310-9956-ffa450edef68