Bug 18501: (QA follow-up) Remove FIXME + Track issue_id

Bug 18501: (QA follow-up) Remove FIXME + Track issue_id

We correct some compilation errors here by updating the transfered
_FixAccountForLostAndFound method to use $self references.  We add
issue_id tracking so that future reports can clearly see how a refund
relates to the original charge and finally we remove a FIXME as I agree
that the 'discard_changes' call is not required.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>