remote-hg: fix path when cloning with tilde expansion

remote-hg: fix path when cloning with tilde expansion

The current code fixes the path to make it absolute when cloning, but
doesn't consider tilde expansion, so that scenario fails throwing an
exception because /home/myuser/~/my/repository doesn't exists:

    $ git clone hg::~/my/repository && cd repository && git fetch

Expand the tilde when checking if the path is absolute, so that we don't
fix a path that doesn't need to be.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>