bundle create: keep symbolic refs' names instead of resolving them

bundle create: keep symbolic refs' names instead of resolving them

When creating a bundle, symbolic refs used to be resolved to the
non-symbolic refs they point to before being written to the list
of contained refs.  I.e. "git bundle create a1.bundle HEAD master"
would show something like

388afe7881b33102fada216dd07806728773c011        refs/heads/master
388afe7881b33102fada216dd07806728773c011        refs/heads/master

instead of

388afe7881b33102fada216dd07806728773c011        HEAD
388afe7881b33102fada216dd07806728773c011        refs/heads/master

Introduce a special handling so that the symbolic refs are listed
with the names passed on the command line.

Noticed by Santi Béjar.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>