debian/.gitignore: add

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

debian/.gitignore

+/*.debhelper.log
+/*.postinst.debhelper
+/*.postrm.debhelper
+/*.preinst.debhelper
+/*.prerm.debhelper
+/*.substvars
+/.debhelper/
+/autoreconf.after
+/autoreconf.before
+/debhelper-build-stamp
+/files
+/gir1.2-traprain-client-0/
+/gir1.2-traprain-common-0/
+/gir1.2-traprain-guidance-0/
+/gir1.2-traprain-service-0/
+/libtraprain-0-doc/
+/libtraprain-0-tests/
+/libtraprain-client-0-0/
+/libtraprain-client-0-dev/
+/libtraprain-common-0-0/
+/libtraprain-common-0-dev/
+/libtraprain-guidance-0-0/
+/libtraprain-guidance-0-dev/
+/libtraprain-service-0-0/
+/libtraprain-service-0-dev/
+/tmp/
+/traprain-mock-service/