Create ~git/gitosis in gitosis-init.

This fixes problems with e.g. "No such file or directory:
'/.../git/gitosis/projects.list.42.tmp'" in generate_project_list when
running gitosis-init.

Existing users need to run::

	 sudo install -d -m0755 -o git -g git ~git/gitosis

adjust the user and group name if necessary. Alternatively,
just rerun gitosis-init.

gitosis/init.py

@@ -125,6 +125,9 @@ class Main(app.App):
             log.error('Cannot parse user from SSH public key.')
             sys.exit(1)
         log.info('Admin user is %r', user)
+        log.info('Creating generated files directory...')
+        generated = util.getGeneratedFilesDir(config=cfg)
+        util.mkdir(generated)
         log.info('Creating repository structure...')
         repositories = util.getRepositoryDir(cfg)
         util.mkdir(repositories)