debian: Add a gbp.conf to start using git-buildpackage

On Bdale Garbee's recommendation I'm switching from gitpkg, (which
constructed a source tree but still required me to go run debuild), to
git-buildpackage. I hadn't originally used git-buildpackage because it
didn't seem to work without a configuration file, (where gitpkg was
fine).

Bdale was kind enough to point me to his fw/altos source at
git.gag.com where I found an example gpb.conf file as well as a target
in debian/rules to automatically update debian/changelog with the new
version number.

.gitignore

@@ -13,3 +13,4 @@ libnotmuch.so*
 .*.swp
 *.elc
 releases
+debian-build

debian/gbp.conf

@@ -0,0 +1,16 @@
+# Configuration file for git-buildpackage
+
+[DEFAULT]
+cleaner = debian/rules prebuild && debuild clean
+
+# The default branch for upstream sources
+upstream-branch = master
+
+# The default branch for the debian patch (no patch in our case)
+debian-branch = master
+
+# Directory for performing the build
+export-dir = ./debian-build
+
+# Format for the debian tag
+debian-tag = debian-%(version)s

debian/rules

@@ -1,4 +1,11 @@
 #!/usr/bin/make -f
+
+# This target invoked by git-buildpackage using a clean hook, see gbp.conf
+prebuild:
+	git-dch --release --new-version=$(VERSION)
+	git commit -n debian/changelog \
+		-m "Automatically update debian/changelog for $(VERSION)"
+
 %:
 	dh $@