Do not call `realpath` in `find_git_toplevel`
Do not call `realpath` in `find_git_toplevel`

git already returns the "real" path when asking for "show-toplevel".

Older Windows versions in fact did not but then `os.path.realpath` is
not implemented in Python 3.3 on Windows.

Use instead the simpler `normpath` to just swap `/` with `\`.

divmain/GitSavvy,divmain/GitSavvy,divmain/GitSavvy