New translation into Dutch for Window Maker

Because the existing nl locale files are ancient and obsolete,
the user interface stays mainly in English with hardly Dutch text
showing up.

This is a complete translation in 6 parts from scratch, using the
current (pl)menus and Makefile generated .pot files. These files
provide a very good, and thoroughly checked user interface in the
Dutch language.

Adding me as a maintainer in related README files; removing previous
maintainer (e-mail bounced).

Removing unnecessary executable bit from pt.po on the fly.

WPrefs.app/po/README

@@ -42,3 +42,4 @@ bg.po	Bulgarian		Slavei Karadjov <slaff@exco.net>
 sk.po   Slovak			Jan 'judas' Tomka <judas@linux.sk>
 et.po	Estonian		Ivar Smolin <okul@linux.ee>
 ca.po	Catalan			Ernest Adrogué <eadrogue@gmx.net>
+nl.po	Dutch			Alwin <translations@ziggo.nl>