emacs config: next-error search path ok even if default-directory unset.
This way next-error behaves accordingly with make -C. Making the setting
of default-directory independent of the compile/next-error setting.


git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16905 85f007b7-540e-0410-9357-904b9bb8a0f7