Think I've messed up X :(

[Andrew Ingram <andrew@uk.clara.net>]

Last week, when I did an apt-get update (I'm on Sid btw), I was told
that:

The following packages have been kept back:
  x-window-system-core xlibmesa-gl-dev xlibmesa-glu-dev 

Now, normally when I see that, I do an apt-get install of the packages
so that apt then tells me it can't install them because of certain
dependencies, which out of curiosity I like to know. This time however,
the upgrade went ahead to my horror. I ctrl-c'd out but it was too late,
the damage had been done. Things seemed to be going ok since then but
today's upgrade required me to downgrade libxft2 to 2.1.2-5 in order to
go through. But I've noticed I'm now stating to have all kinds of nasty
stuff happening with fonts (ie not showing any text at all) and windows
are appearing with hardly any height, but massive width (again, no
text). Opening Konqueror for example shows no menu bar, just some
horizontal black lines and there is no text anywhere. Kate just crashes,
etc.

I am a bit too scared to do a reboot as I have a feeling it will only
make things worse. Is there a way out of this? In order to get into this
mess, I did:
apt-get install xlibmesa-dri xlibmesa-gl xlibmesa-gl-dev xlibmesa-glu
xlibmesa-glu-dev
which removed:
xlibmesa3-gl xlibmesa3-glu

I'd really appreciate some help as I dont fancy having to re-install
X/KDE from scratch.

Regards,
Andrew