Merge r291480 from trunk:

* Makefile.in
  (docs): If the "docs-build" project is available, trigger its build system
   to turn the XML sources into HTML.  Otherwise, display a URL to the
   instructions on how to use the docs build.

* build/rules.mk.in:
  (.PHONEY): docs is a fake target.

Submitted By: Daniel Rall <dlr apache.org>
Reviewed by: pquerna


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@291485 13f79535-47bb-0310-9956-ffa450edef68