[Dune] Bugfix for problem with parallel UG

[Oliver Sander]

Dear Dune!
Various people have recently reported problems with the AutoTools
MPI test in UG with the patch file 3.9.1-patch3.  Christian has fixed
a bug and I have prepared a new patch file -patch4.  Please use this
patch file from now on and report back if there are further problems.

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OS

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* Oliver Sander                ** email: sander at mi.fu-berlin.de        *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75348           *
* Institut für Mathematik      ** URL  : page.mi.fu-berlin.de/~sander  *
* Arnimallee 6                 ** -------------------------------------*
* 14195 Berlin, Germany        ** Member of MATHEON (www.matheon.de)   *
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