git-pw: Recurse with newer versions of GitPython

Ander noticed we didn't actually recurse, and that

    commit 7403987
    Author: Damien Lespiau <damien.lespiau@intel.com>
    Date:   Wed Nov 11 12:42:05 2015 +0000

    git-pw: Make git-pw work with older versions of GitPython

was too hopeful in its expectations (I swear it was true at the time?
but may have been fooled).

v2: Use git.__version__ to decide when to include the
    search_parent_directories named argument.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

git-pw/git-pw

@@ -497,9 +497,27 @@ class GitPatchwork(object):
     def __init__(self):
         self.cmd = Command()
 
+    def _git_python_version(self):
+        # remove anything after a first space ('0.3.2 RC1' -> '0.3.2')
+        version = git.__version__.split()[0]
+        # return (major, minor, path)
+        return tuple(map(int, version.split('.')))
+
+    def _create_repo(self, path):
+        # we want to recurse through parent directories:
+        #   - early versions of GitPython's Repo constructor doesn't have the
+        #     search_parent_directories named argument, but do recurse
+        #   - at some point, GitPython introduced said argument and defaults
+        #     to non-recursive. Only try that if the first call fails to
+        #     create the repo object
+        if self._git_python_version() >= (0, 3, 5):
+            return git.Repo(os.getcwd(), search_parent_directories=True)
+        else:
+            return git.Repo(os.getcwd())
+
     def setup(self):
         try:
-            self.repo = git.Repo(os.getcwd())
+            self.repo = self._create_repo(os.getcwd())
         except git.exc.InvalidGitRepositoryError:
             if self.cmd.need_git_repo:
                 die('Not a git repository.')