contrib/docker/fedora20

transaction: pass the transaction to 'pending' callback

The callback will likely need to perform some operation related to the
transaction (eg: backing files up). So we better pass the current transaction as
the callback argument. Otherwise callback that needs it has to rely on horrible
weak reference trick.

The first foreseen user of this is changelog._writepending. We would like it to
register the temporary file it create for cleanup purpose.

FROM fedora:20
RUN yum install -y gcc
RUN yum install -y python-devel python-docutils
RUN yum install -y make
RUN yum install -y rpm-build
RUN yum install -y gettext
# For creating repo meta data
RUN yum install -y createrepo