upgrade-prep: don't remove boot entry if testing

It's pretty common for me to run the upgrade in test mode, see that
everything is working, and then run it for real. Removing the boot entry
makes that tougher than it needs to be, so leave it alone when we're
testing.
po: update POTFILES.in, add Makefile

I keep forgetting how to regenerate fedup.pot, so here we go.
sysprep: drop 'plymouth.splash=fedup'

As the comment says, we can drop this now that the plymouth patch is
upstream and built (see plymouth commit a9703fb).
Fix misleading free space message (#949963)

If you've got 1.5G free but you're 260M short, the old message was:
  need 260M free on / (1.5G free)
which can be confusing: "So I need 260M, but I have 1.5G free?"

The new message is more direct:
  / needs 260M more free space
TODO: Fix incorrect bugzilla URL etc.
code cleanups for commandline.py

Also slight tweaks to a couple of help strings.
cli: add --enableplugin/--disableplugin

Some plugins have been causing trouble for fedup. Allow the user to
manually enable/disable them so they can work around their wonky
plugins.
Complain about broken plugins

If a yum plugin raises an uncaught exception, we should tell the user
which plugin is causing the problem. This way they can disable it with
--disableplugin and they know who to complain to about the problem.
make system-upgrade.target work with newer systemd (#954371)

We don't need to wait for udev specifically, since newer sysinit.target
will pull that in for us. And since udev.service has changed to
systemd-udev.service, if we Require that we can never make it to our
default target, and then we're hosed.
Fix emergency shell on F17 upgrades (#958586)

F17 systemd startup stuff still needs udev services to be explicitly
pulled in, or else we'll get dumped into emergency mode.
Fix GUI startup problem in fedup.commandline

The check for the SOURCE arg traces back in GUI mode because there's no
args.clean (because the gui doesn't handle --clean).

But also: the GUI doesn't require a SOURCE arg. So skip the rest of that
check in GUI mode.
Handle None from _downloadPackages (#949725)

YumBase._downloadPackages returns a list, unless it finds no updates, in
which case it returns None. Convert this return value to an empty list
so that the value can always be converted to a set.
Handle KeyboardInterrupt during download (#961955)

FedupDownloader.download_boot_images checks for IOErrors that are raised
as KeyboardInterrupt in older versions of yum.urlgrabber. This change
adds the other half of the conditional: if a KeyboardInterrupt is raised
and a newer urlgrabber is in use, raise the exception as-is.
fedup.util: add missing 'log' variable (#966841)

fedup.util didn't have any way to log anything, but rm_f wanted to log
(and ignore) failures, so if it couldn't remove a file you'd get a
traceback instead of a log message. oops.
log creation of module dir

Also, a minor cleanup for an unneeded double call to kernelver()
Umount ISO image before raising SystemExit(1)

When ISO file is not the required DVD install, we should umount the mount point
before raising the exception.

Fix bug https://bugzilla.redhat.com/show_bug.cgi?id=981076
clarify "instrepo not found" error (#980818 et. al)

The existing error message didn't make clear that you probably just need
to try again later ('cuz the mirrors are overloaded and/or you're
jumping the gun on the release).
Update TODO
README: add details about network upgrades

This should be helpful for repo maintainers and/or anyone else who is
curious/confused about how fedup finds the repos and images it uses.
Merge pull request #7 from mopsfelder/umount-iso

Umount ISO image before raising SystemExit(1)