Make build-dependency on git optional, since it's not available on all platforms and only used for the testsuite.

debian/changelog

@@ -1,3 +1,10 @@
+dulwich (0.18.1-2) UNRELEASED; urgency=medium
+
+  * Make build-dependency on git optional, since it's not available on
+    all platforms and only used for the testsuite.
+
+ -- Jelmer Vernooij <jelmer@debian.org>  Mon, 31 Jul 2017 22:21:12 +0000
+
 dulwich (0.18.1-1) unstable; urgency=medium
 
   * New upstream release.

debian/control

@@ -4,7 +4,7 @@ Priority: optional
 Maintainer: Debian Python Modules Team <python-modules-team@lists.alioth.debian.org>
 Uploaders: Jelmer Vernooij <jelmer@debian.org>
 Homepage: https://www.dulwich.io/
-Build-Depends: python-all-dev (>= 2.6.6-3), python-all-dbg (>= 2.6.6-3), python3-all-dev, python3-all-dbg, debhelper (>= 9.20160114), python-unittest2, git (>= 1:1.7.0.4-2) | git-core, python-fastimport (>= 0.9.0~bzr293), python3-fastimport, pypy-dev [!hurd-any !m68k !sh4 !x32], dh-python
+Build-Depends: python-all-dev (>= 2.6.6-3), python-all-dbg (>= 2.6.6-3), python3-all-dev, python3-all-dbg, debhelper (>= 9.20160114), python-unittest2, git (>= 1:1.7.0.4-2) | git-core | dpkg, python-fastimport (>= 0.9.0~bzr293), python3-fastimport, pypy-dev [!hurd-any !m68k !sh4 !x32], dh-python
 Standards-Version: 4.0.0
 X-Python-Version: >= 2.7
 X-Python3-Version: >= 3.2