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)