Add a fastimport 'extra'.

NEWS

@@ -9,6 +9,10 @@
   * Allow comment characters (#, ;) within configuration file strings
     (Daniel Andersson, #579)
 
+ IMPROVEMENTS
+
+  * Add a fastimport ``extra``. (Jelmer Vernooij)
+
 0.18.6	2017-11-11
 
  BUG FIXES

setup.py

@@ -109,6 +109,9 @@ setup(name='dulwich',
           'Operating System :: Microsoft :: Windows',
           'Topic :: Software Development :: Version Control',
       ],
+      extras_require={
+          'fastimport': ['fastimport'],
+      },
       ext_modules=ext_modules,
       test_suite='dulwich.tests.test_suite',
       tests_require=tests_require,