Refreshed pnd_run and sudoers scripts from wiki

Refreshed pnd_run and sudoers scripts from wiki
Added support for 'no_x11' option in PXML.xml (and subsequently in emit_dotdesktop and pnd_apps_exec)
	-> untested
Added pnd_pnd_mount and pnd_pnd_unmount in pnd_pndfiles, so apps can mount and find screenshots and such
	-> untested
Added basic validator app (doesn't do anything, we need to add some regexp's in there!)
Added some new element names in pnd_pxml_names etc for the tinyxml parser