List all the debian build dependencies

These have been tested on a debootstrap based install of
debian wheezy.

The gettext dependency is only required for some m4 macros
used in m4/iconv.m4 - to avoid it, the lib-prefix.m4 and
lib-link.m4 files from gettext could be bundled as well.
Merge pull request #4 from mstorsjo/debian-deps

List all the debian build dependencies