Two feature ideas for diffs

[Tom <adatgyujto@gmail.com>]

I was reading this description of PyCharm 

   http://nicoddemus.github.io/articles/pycharm/

and there was two features described which could be useful in
emacs too.

The first is diff indicators in the sidebar. If the file is under
version control and it is edited then a mark appears beside the
changed lines and if it is clicked then you can see what's
changed in the line or in that hunk, you don't have to do a full
file diff which may contain many other changes unrelated to the
current line. You can also rollback that particular change,
etc. Is there something like this for emacs? If not it could be a
useful addition.

The other interesting feature is editable diffs. So, for example,
before checking in one usually does a diff to see what was
changed in the file. If you notice a typo then you go back to the
file, fix it, do a diff again to check the changes, etc. PyCharm
lets you edit the diff instead, so if you made a typo then you
can fix it in the diff buffer and it is applied to the original
file. It would be a nice convenience feature.