fix traceback for transaction problems with one package (#1047005)

It's possible that pkg2 will be None here, so we need to handle that
case without crashing.
fedup.spec: make sure we have the required systemd version

system-upgrade-generator requires systemd v183 or higher, so make sure
we have a new enough systemd.

This will make fedup 0.8.x unable to install on F17, which is fine since
it doesn't currently work there.
Add version to fedup log message

This requires fedup to know what version it is, so add version.py.. and
for the sake of simplicity, add a 'make version' target that will write
the version in the Makefile into the places it needs to go when we bump
the version.