Add incremental blame support

This adds a sibling method to Repo's blame method:

    Repo.blame_incremental(rev, path, **kwargs)

This can alternatively be called using:

    Repo.blame(rev, path, incremental=True)

The main difference is that blame incremental is a bit more efficient
and does not return the full file's contents, just the commits and the
line number ranges.  The parser is a bit more straight-forward and
faster since the incremental output format is defined a little stricter.

1 files changed, 15 insertions, 0 deletions

diff --git a/git/compat.py b/git/compat.py
index 1ea2119e..146bfd4b 100644
--- a/git/compat.py
+++ b/git/compat.py
@@ -8,6 +8,7 @@
 # flake8: noqa
 
 import sys
+import six
 
 from gitdb.utils.compat import (
     PY3,
@@ -46,6 +47,20 @@ else:
     def mviter(d):
         return d.itervalues()
 
+PRE_PY27 = sys.version_info < (2, 7)
+
+
+def safe_decode(s):
+    """Safely decodes a binary string to unicode"""
+    if isinstance(s, six.text_type):
+        return s
+    elif isinstance(s, six.binary_type):
+        if PRE_PY27:
+            return s.decode(defenc)  # we're screwed
+        else:
+            return s.decode(defenc, errors='replace')
+    raise TypeError('Expected bytes or text, but got %r' % (s,))
+
 
 def with_metaclass(meta, *bases):
     """copied from https://github.com/Byron/bcore/blob/master/src/python/butility/future.py#L15"""