[Dune] UGGrid in libdune

[Oliver Sander]

Hi guys!
I extended the dune build system a bit so that now the two instantiations
dim==dimworld==2 and dim==dimworld==3 of the UGGrid class are precompiled 
in libdune.  These are the only ones possible anyways.
The main reason I did this is the following:  UGGrid uses a few static
variables.  If their definition is #included into every compilation unit
(as was the case so far) you get multiple-definition linker errors when
trying to link objects files together with more than one using UGGrid.
As the static variables are defined _once_ now, namely in libdune, this
problem is fixed.
Now, if you want to use UGGrid, you have to supply the option
--with-ug=my_ug_path when configuring DUNE.  You do _not_ have to
supply the problem-dim/world-dim options, as 'all' possible instantiations
of UGGrid are compiled anyways.

Enjoy!
Oliver

************************************************************************
* Oliver Sander                **                                      *
* Freie Universität Berlin     ** email: sander at math.fu-berlin.de      *
* Institut für Mathematik II   ** phone: + 49 (30) 838 75217           *
* Arnimallee 2-6               ** fax  : + 49 (30) 838 54977           *
* 14195 Berlin, Germany        ** URL  : www.math.fu-berlin.de/~sander *
************************************************************************