dh-exec-filter: Correctly handle postfix arch filters

Use a regexp that does not match newlines when removing the arch
filters. This makes postfix filters work.

Reported-by: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
t: Fix the name of the filter tests

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
dh-exec-install: Work on .manpages files too

Teach dh-exec-install to also work on .manpages file. The output is not
quite correct yet, that will come in a followup patch.

Requested-by: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
dh-exec-install-rename: dh_installmanpages support

When the DH_EXEC_SOURCE environment variable ends in "manpages", do not
append the destination directory. The dh_installmanpages script will
figure that out nicely.

Closes: Debian#757270
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>