dh: Add support for build-arch, build-indep, install-arch and install-indep sequences

dh: Add support for build-arch, build-indep, install-arch and install-indep sequences

The existing binary-arch and binary-indep sequences depend upon these
new sequences, leading to the following possible orders:

binary → install → build
binary-arch → install-arch → build-arch
binary-indep → install-indep → build-indep

This is the logical dependency ordering of the sequences; the actual
order is of course in reverse so that build is followed by install
and binary.

Signed-off-by: Roger Leigh <rleigh@debian.org>