Here are some updates for the xapian-bindings packaging, introducing
python3-xapian. In general, the packaging could need an update. It doesn't have
to be debhelper 9, but some things could be fixed.

I didn't address:

 - python and python3 docs are installed into the same place, so
   the current way installing the docs into the same temp dir
   doesn't work.

 - The docs build try to import the just built bindings, and fail
   to find these. I assume this is an upstream error.

For now my experimental python3-xapian package is good enough for testing things.

Control: fixed 1.4.0-2

I think this is the first time I've seen this bug despite it being filed
10 years ago.  It seems this was filed against a non-existant source
package and anbe recently noticed and reassigned it (and some other bugs
in a similar situation).

I looked through and all the points this addresses seem to have been
addressed long ago - most of them by a switch to dh in 1.4.0-2 in
2016 so marking as fixed in that version, though that may not be
completely right.

Cheers,
    Olly