safe.directory: normalize the checked path

safe.directory: normalize the checked path

The pathname of a repository comes from getcwd() and it could be a
path aliased via symbolic links, e.g., the real directory may be
/home/u/repository but a symbolic link /home/u/repo may point at it,
and the clone request may come as "git clone file:///home/u/repo/".

A request to check if /home/u/repo is safe would be rejected if the
safe.directory configuration allows /home/u/repository/ but not its
alias /home/u/repo/.  Normalize the path being checked before
comparing with safe.directory value(s).

Suggested-by: Phillip Wood <phillip.wood123@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>