init: make --template path relative to $CWD

init: make --template path relative to $CWD

During git-init we chdir() to the target directory, but --template is
not adjusted. So it's relative to the target directory instead of
current directory.

It would be ok if it's documented, but --template in git-init.txt
mentions nothing about this behavior. Change it to be relative to $CWD,
which is much more intuitive.

The changes in the test suite show that this relative-to-target behavior
is actually used. I just hope that it's only used in the test suite and
it's safe to change. Otherwise, the other option is just document
it (i.e. relative to target dir) and move on.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>