bug#18698: Our WindowMaker wrapper pollutes PATH in the entire X session

[Ricardo Wurmus]

The fix may have resulted in unintended side-effects.  On a fresh
installation of the System Distribution v0.8.1 WindowMaker is installed
by default, but it is not completely functional.

For example, the attempt to change the style via the menu results in
this error to be displayed:

    Could not execute command:
        setstyle 
/gnu/store/...windowmaker.../share/WindowMaker/Styles/Black.style

Likewise, selecting "Configure Window Maker" from the right-click menu
results in this error:

    Could not execute command: exec WPrefs

The "setstyle" executable is located in
/gnu/store/...windowmaker.../bin/, but is not in the PATH.

~~ Ricardo