Revert "session: drop remnants of WINDOWPATH"

This reverts commit 6e1f486ca0d37da9fc8239493633deed6d796b93.

https://bugzilla.gnome.org/show_bug.cgi?id=730729
Revert "slave: Remove support for WINDOWPATH"

This reverts commit 64210ac9dc1dafd1970ad0abcf46a010731d17b4.

https://bugzilla.gnome.org/show_bug.cgi?id=730729
doap category core