Split off the Gnome MDB file viewer into its own project:
https://github.com/mdbtools/gmdb2
This simplifies the build process somewhat and lets us focus on the core
project. (For starters, no more -Wno-portability flag!)
The existing iconv.m4 warns against using a serial version, but adding
an empty config.rpath to build-aux/ should make it work just fine.
The new version should work better on various less-popular platforms.
'gnome-doc-utils' is a rather large dependency on OS X, and the build
system has checks for gnome-doc-utils surrounding its use, but the
autoconf check errors out in its absence.
