rename a remote does not update pushdefault (v1.9.5)

When defining pushdefault and renaming the associated remote, the pushdefault setting becomes invalid. Instead, it should follow the renamed remote if that was designated as pushdefault.

Test procedure:

1. Create/cd empty directory
2. `git init .`
3. `git remote add abc def`
4. Observe that `git remote` now shows 'abc'
5. `git config default.pushdefault abc`
6. Observe that `git config --list` shows default.pushdefault=abc
7. `git remote rename abc xyz`

BUG: observe that pushdefault still refers to 'abc', while it should now refer to 'xyz'.

Rgds

(Initially (wrongly) filed as TGit bug: https://code.google.com/p/tortoisegit/issues/detail?id=2438)