Fixes <http://bugs.gnu.org/19364>.
Reported by Tomáš Čech <sleep_walker@suse.cz>
and Mark H Weaver <mhw@netris.org>.
* gnu/packages.scm (%patch-path): Move after definition of
%package-module-path'. Append "/gnu/packages/patches" only to
%DISTRO-ROOT-DIRECTORY.
* tests/guix-package.sh: Add 'emacs-foo-bar-patched' test.