Numerous fixes and changes

Numerous fixes and changes
- a fix to invokers of the pnd_locate_filename function; you must strdup() the result .. otherwise multiple invocations will
  return the same buffer, and thus all references will change simultaneously
- nohup is only put into Exec= line .desktop if it is also a no-x11 app (most apps should be x11 I imagine, using SDL?)
- Icons for .desktops can be placed anywhere; path is configured .. 'iconpath' key; nolonger assumed to be same location
  as .desktop's go to
- updated config files to include iconpath (test goes to testdata/dotdesktop for now); production goes to /tmp for now
- updated config files so .desktop goes to ~/Desktop for production
- updated config files to comment out pnd_hup script, as xfce appears not to need it. (it may be re-enabled should we switch WMs)