Minor Bug in Renaming Branches

Hi,

Not quite sure where to submit bug reports about Git, this was the best I could find, so if there's a better place to do this, please let me know and I will.

The short of this issue is that on Mac and Windows, if a branch has a slash in its name, changing it from lowercase to uppercase requires diving into .git/refs/heads/ and manually moving stuff around - I think the behavior should be at least something like this: http://stackoverflow.com/questions/26810252/how-to-change-my-local-github-branch-name-to-uppercase.

It happens that on both Windows box, to rename a branch from
"branch/name" to "BRANCH/NAME", one has to actually dive into
.git/refs/heads/ because of how Windows handles upper/lowercase in
directory paths. (Win7, mingw64 via Git for Bash, git version
2.7.0.windows.1)
user@windows-box MINGW64 ~
$ mkdir sandbox && cd sandbox && git init
Initialized empty Git repository in C:/Users/user/sandbox/.git/
user@windows-box MINGW64 ~/sandbox (master)
$ touch empty.txt && git add empty.txt && git commit -m 'initialize repo'
[master (root-commit) 761113d] initialize repo
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 empty.txt
user@windows-box MINGW64 ~/sandbox (master)
$ git branch
* master
user@windows-box MINGW64 ~/sandbox (master)
$ git checkout -b branch/name
Switched to a new branch 'branch/name'
user@windows-box MINGW64 ~/sandbox (branch/name)
$ git branch
* branch/name
  master
user@windows-box MINGW64 ~/sandbox (branch/name)
$ git branch -m BRANCH/NAME
fatal: A branch named 'BRANCH/NAME' already exists.
user@windows-box MINGW64 ~/sandbox (branch/name)
$ git branch -m tmp
user@windows-box MINGW64 ~/sandbox (tmp)
$ git branch -m BRANCH/NAME
user@windows-box MINGW64 ~/sandbox (BRANCH/NAME)
$ git branch
  branch/NAME
  master
user@windows-box MINGW64 ~/sandbox (BRANCH/NAME)
$ mv .git/refs/heads/branch/ .git/refs/heads/BRANCH/
user@windows-box MINGW64 ~/sandbox (BRANCH/NAME)
$ git branch
* BRANCH/NAME
  master

Interestingly, from inside an Ubuntu VM (with the directory in question mounted as a VBox fileshare), this is not an issue.

A colleague on a Mac also reproduces the issue successfully (OSX 10.11.5, git 2.8.3):

mac-box:sandbox user$ touch empty.txt && git add empty.txt && git
commit -m 'initial commit'
[master (root-commit) 1f4f1fa] initial commit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 empty.txt
mac-box:sandbox user$ git branch
* master
mac-box:sandbox user$ git checkout -b branch/name
Switched to a new branch 'branch/name'
mac-box:sandbox user$ git branch -m BRANCH/NAME
fatal: A branch named 'BRANCH/NAME' already exists.
mac-box:sandbox user$ git branch
* branch/name
  master
mac-box:sandbox user$ git branch -m tmp
mac-box:sandbox user$ git branch
  master
* tmp
mac-box:sandbox user$ git branch -m BRANCH/NAME
mac-box:sandbox user$ git branch
  branch/NAME
  master
mac-box:sandbox user$ mv .git/refs/heads/branch/ .git/refs/heads/BRANCH/
mac-box:sandbox user$ git branch
* BRANCH/NAME
  master

Thanks, Sam