tests/test-docker-packaging.t

debian: switch to using debhelper and dh_python2 to build debs

This is a much larger commit than I'd like, but I honestly don't see a
good way to break it up and leave things working. Summary:

We now use debian/rules with debhelper to build our debs. This is much
more standard, and means we use dh_python2 to do things like handle
leaving .pyc files out of the built debs.

The resulting package is split into mercurial and mercurial-common,
with the former being the hg stub and all the native .sos, and the
latter being basically everything else.

builddeb and dockerdeb are updated to use the new system. The old way
(using dpkg by hand) breaks with the above changes because
debian/control no longer contains a version string (that's now guessed
from the phony changelog.)

Tests are updated to assert that the right files end up in the right
debs.

#require test-repo slow docker

Ensure debuild doesn't run the testsuite, as that could get silly.
  $ DEB_BUILD_OPTIONS=nocheck
  $ export DEB_BUILD_OPTIONS
  $ OUTPUTDIR=`pwd`
  $ export OUTPUTDIR

  $ cd "$TESTDIR"/..
  $ make docker-debian-jessie > $OUTPUTDIR/build.log 2>&1
  $ cd $OUTPUTDIR
  $ ls *.deb
  mercurial-common_*.deb (glob)
  mercurial_*.deb (glob)

We check debian package contents with portable tools so that when
we're on non-debian machines we can still test the packages that are
built using docker.

main deb should have .so but no .py
  $ ar x mercurial_*.deb
  $ tar tf data.tar* | egrep '(localrepo|parsers)'
  ./usr/lib/python2.7/dist-packages/mercurial/parsers*.so (glob)
mercurial-common should have .py but no .so or .pyc
  $ ar x mercurial-common_*.deb
  $ tar tf data.tar* | egrep '(localrepo|parsers)'
  ./usr/lib/python2.7/dist-packages/mercurial/localrepo.py