[Dune] Bug in AluGrid entity assignment operator

[Oliver Sander]

Dear Dune!
Could please somebody who knows be so kind and fix bug 147?  It
keeps me from completing the elasticity problem for our paper.

Yes, I know, the assignment operator in ALUGrid is a hairy
issue, but I happen to use them.  And since the whole point
of that section of the paper is that I claim to have switched
between grids without having changed my program I think I
should be allowed to keep the assignment operator in it.

merry evening, folks!
Oliver

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* Oliver Sander                ** email: sander at mi.fu-berlin.de        *
* Freie Universität Berlin     ** phone: + 49 (30) 838 75217           *
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