Handle symlinks graciously

Handle symlinks graciously

This patch converts a stat() to an lstat() call, thereby fixing the case
when the date of a symlink was not the same as the one recorded in the
index. The included test case demonstrates this.

This is for the case that the symlink points to a non-existing file. If
the file exists, worse things than just an error message happen.

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>