[patch] Use $PATH for desktop

[glixx]

If to put douml.desktop on the Desktop (KDE), then it's not visible with TryExec=douml. And we should use $PATH for desktop file.

[glixx]

There is patch from Mageia Linux: http://svnweb.mageia.org/packages/cauldron/douml/current/SOURCES/douml-1.0-mga-exec-desktop.patch?view=markup&pathrev=659007