fix "make install" directory-creation stuff

This has been broken since it was first implemented in fae09b19
almost a year ago.  I guess the problem has mostly been masked
by distro packaging and/or runtime mkdir stuff, but this at least
gets rid of the pointless "system" directory created by the bug.
Merge branch 'master' into 2.x
Merge branch '2.x' into dmn-rework