Build-depend on automake, autoconf, libtool and pkg-config. Drop patch for
maintainer mode, and drop build-dep on quilt and corresponding code in
debian/rules. Add new rules autogen and config, where we run autoreconf and
configure, respectively. Update clean rule to remove files generated by
autogen.
This prevents gcc 4.2 from generating SSE instructions for its builtin
functions, the X server from going SIGILL on CPUs supporting MMX but not SSE,
and us from losing (closes: #442829).
Also enable maintainer mode in configure.ac so we can carry the patch to
configure directly in the diff.gz without running autoreconf at build time.