source download link in installation instructions

The installation instructions in the devel branch

http://www.postgresql.org/docs/devel/static/install-getsource.html

contain a direct link to the tarball download

ftp://ftp.postgresql.org/pub/source/v9.3devel/postgresql-9.3devel.tar.gz

which doesn't exist.  It will presumably exist once there is a final
release, but I think it's bad to have that link broken in the meantime,
especially when beta comes around.  It's also not clear whether ftp and
tar.gz are necessarily the preferred download means anymore.

Should we just provide a link to http://www.postgresql.org/download/ or
http://www.postgresql.org/ftp/source/ instead?  Or perhaps just "ifdef"
out the broken link in the devel versions?