setup: added missing _delta_apply.c file to setup script, allowing the performance module to be compiled

Author: Byron

setup.py

@@ -77,7 +77,7 @@ def get_data_files(self):
       package_data={'gitdb' : ['AUTHORS', 'README'], 
 					  'gitdb.test' : ['fixtures/packs/*', 'fixtures/objects/7b/*']},
       package_dir = {'gitdb':''},
-      ext_modules=[Extension('gitdb._perf', ['_fun.c'])],
+      ext_modules=[Extension('gitdb._perf', ['_fun.c', '_delta_apply.c'])],
       license = "BSD License",
       requires=('async (>=0.6.1)',),
       install_requires='async >= 0.6.1',