Add a trigger to (un)register system user/groups.

The following vars can be used for this:

- system_accounts="foo blah"
- foo_homedir, foo_shell, foo_descr, foo_groups.

--HG--
extra : convert_revision : bc7d002e00abc5c84f83a3716a8ecf97f9c9ff24

xbps-src/triggers/Makefile

@@ -3,6 +3,7 @@ include ../vars.mk
 TRIGGERS=	gtk-icon-cache info-files mimedb register-shell
 TRIGGERS+=	xml-catalog gtk-immodules initramfs-tools openrc-service
 TRIGGERS+=	update-desktopdb gtk-pixbuf-loaders pango-modules x11-fonts
+TRIGGERS+=	system-accounts
 
 .PHONY: all
 all: