Make build reproducible

https://wiki.debian.org/ReproducibleBuilds

Author: onovy

setup.py

@@ -72,7 +72,7 @@
 
 libgit2_bin, libgit2_include, libgit2_lib = get_libgit2_paths()
 
-pygit2_exts = [os.path.join('src', name) for name in listdir('src')
+pygit2_exts = [os.path.join('src', name) for name in sorted(listdir('src'))
                if name.endswith('.c')]