build: Make autogen.sh work

build: Make autogen.sh work

* We were missing a call to gettextize, which is what copies in config.rpath
* Delete ABOUT-NLS, it is copied in by gettextize
* While we're here, take a page from gtk+'s autogen.sh and just use autoreconf,
  instead of specifying everything.
* We need to always have an m4/ directory, so that gettextize works,
  so we make a dummy empty file
* Apparently gettextize is totally insane, requiring user input etc.  Copy
  in some hacks from Avahi's autogen.sh to work around this.