fix(index): don't write extension data by default

It turned out that the index is not actually corrupted, which is good
news. What happens is that `git` writes `TREE` extension data into the
index, which causes it to write out the given tree *as is* next time
a `git commit` is executed. When using `git add`, this extension data
is maintained automatically. However, GitPython doesn't do that ... .
Usually this is no problem at all, as you are supposed to use
`IndexFile.commit(...)` along with `IndexFile.add(...)`.

Thanks to a shortcoming in the GitPython API, the index was
automatically written out whenever files have been added, without
providing control over whether or not *extension data* will be
written along with it.

My fix consists of an additional flag in `IndexFile.add(...)`, which
causes extension data not to be written by default, so commits can be
safely done via `git commit` or `IndexFile.commit(...)`.

However, this might introduce new subtle bugs in case someone is
relying on extension data to be written. As this can be controlled
through the said flag though, a fix is easily done in that case.

Fixes #265

1 files changed, 6 insertions, 0 deletions

diff --git a/doc/source/changes.rst b/doc/source/changes.rst
index 5b85e56a..52d70c0f 100644
--- a/doc/source/changes.rst
+++ b/doc/source/changes.rst
@@ -2,6 +2,12 @@
 Changelog
 =========
 
+0.3.7 - Fixes
+=============
+* `IndexFile.add()` will now write the index without any extension data by default. However, you may override this behaviour with the new `write_extension_data` keyword argument.
+
+  - Renamed `ignore_tree_extension_data` keyword argument in `IndexFile.write(...)` to `ignore_extension_data`
+
 0.3.6 - Features
 ================
 * **DOCS**