Fix bug in diff parser outputfix-octal-escaped-path-parser-bug

The diff --patch parser was missing some edge case where Git would
encode non-ASCII chars in path names as octals, but these weren't
decoded properly.

    \360\237\222\251.txt

Decoded via utf-8, that will return:

    💩.txt

4 files changed, 31 insertions, 8 deletions

diff --git a/doc/source/changes.rst b/doc/source/changes.rst
index 928675d0..dd7a3815 100644
--- a/doc/source/changes.rst
+++ b/doc/source/changes.rst
@@ -5,6 +5,8 @@ Changelog
 2.0.4 - Fixes
 =============
 
+* Fix: non-ASCII paths are now properly decoded and returned in
+  ``.diff()`` output
 * Fix: `RemoteProgress` will now strip the ', ' prefix or suffix from messages.
 * API: Remote.[fetch|push|pull](...) methods now allow the ``progress`` argument to
   be a callable. This saves you from creating a custom type with usually just one
diff --git a/git/diff.py b/git/diff.py
index 44a65017..9073767e 100644
--- a/git/diff.py
+++ b/git/diff.py
@@ -15,12 +15,23 @@ from git.compat import (
     PY3
 )
 
-
 __all__ = ('Diffable', 'DiffIndex', 'Diff', 'NULL_TREE')
 
 # Special object to compare against the empty tree in diffs
 NULL_TREE = object()
 
+_octal_byte_re = re.compile(b'\\\\([0-9]{3})')
+
+
+def _octal_repl(matchobj):
+    value = matchobj.group(1)
+    value = int(value, 8)
+    if PY3:
+        value = bytes(bytearray((value,)))
+    else:
+        value = chr(value)
+    return value
+
 
 def decode_path(path, has_ab_prefix=True):
     if path == b'/dev/null':
@@ -32,6 +43,8 @@ def decode_path(path, has_ab_prefix=True):
                           .replace(b'\\"', b'"')
                           .replace(b'\\\\', b'\\'))
 
+    path = _octal_byte_re.sub(_octal_repl, path)
+
     if has_ab_prefix:
         assert path.startswith(b'a/') or path.startswith(b'b/')
         path = path[2:]
@@ -337,7 +350,7 @@ class Diff(object):
         :note: This property is deprecated, please use ``renamed_file`` instead.
         """
         return self.renamed_file
-        
+
     @property
     def renamed_file(self):
         """:returns: True if the blob of our diff has been renamed
diff --git a/git/test/fixtures/diff_patch_unsafe_paths b/git/test/fixtures/diff_patch_unsafe_paths
index 14375f79..9ee6b834 100644
--- a/git/test/fixtures/diff_patch_unsafe_paths
+++ b/git/test/fixtures/diff_patch_unsafe_paths
@@ -61,6 +61,13 @@ index 0000000000000000000000000000000000000000..eaf5f7510320b6a327fb308379de2f94
 +++ "b/path/¯\\_(ツ)_|¯"
 @@ -0,0 +1 @@
 +dummy content
+diff --git "a/path/\360\237\222\251.txt" "b/path/\360\237\222\251.txt"
+new file mode 100644
+index 0000000000000000000000000000000000000000..eaf5f7510320b6a327fb308379de2f94d8859a54
+--- /dev/null
++++ "b/path/\360\237\222\251.txt"
+@@ -0,0 +1 @@
++dummy content
 diff --git a/a/with spaces b/b/with some spaces
 similarity index 100%
 rename from a/with spaces
diff --git a/git/test/test_diff.py b/git/test/test_diff.py
index 1d7a4fda..8966351a 100644
--- a/git/test/test_diff.py
+++ b/git/test/test_diff.py
@@ -161,16 +161,17 @@ class TestDiff(TestBase):
         self.assertEqual(res[6].b_path, u'path/with spaces')
         self.assertEqual(res[7].b_path, u'path/with-question-mark?')
         self.assertEqual(res[8].b_path, u'path/¯\\_(ツ)_|¯')
+        self.assertEqual(res[9].b_path, u'path/💩.txt')
 
         # The "Moves"
         # NOTE: The path prefixes a/ and b/ here are legit!  We're actually
         # verifying that it's not "a/a/" that shows up, see the fixture data.
-        self.assertEqual(res[9].a_path, u'a/with spaces')       # NOTE: path a/ here legit!
-        self.assertEqual(res[9].b_path, u'b/with some spaces')  # NOTE: path b/ here legit!
-        self.assertEqual(res[10].a_path, u'a/ending in a space ')
-        self.assertEqual(res[10].b_path, u'b/ending with space ')
-        self.assertEqual(res[11].a_path, u'a/"with-quotes"')
-        self.assertEqual(res[11].b_path, u'b/"with even more quotes"')
+        self.assertEqual(res[10].a_path, u'a/with spaces')       # NOTE: path a/ here legit!
+        self.assertEqual(res[10].b_path, u'b/with some spaces')  # NOTE: path b/ here legit!
+        self.assertEqual(res[11].a_path, u'a/ending in a space ')
+        self.assertEqual(res[11].b_path, u'b/ending with space ')
+        self.assertEqual(res[12].a_path, u'a/"with-quotes"')
+        self.assertEqual(res[12].b_path, u'b/"with even more quotes"')
 
     def test_diff_patch_format(self):
         # test all of the 'old' format diffs for completness - it should at least