#4 Change of reference phi_ to const breaks setValues in faMatrix

[Bernhard Gschaider]

During compilation of swak the const reference phi in faMatrix breaks the instantiation of the setValues-method of that class. This is defintely a problem of the finiteArea-library. It is not seen during the regular foam-extend compilation because setValues is never instantiated in foam-extend as far as I can tell.

I've added two different patches that fix this:
- one const_casts the access to phi in setValues. This has the minimal influence on the rest of the code but I always feel a bit dirty when const_casting because I'm breaking a promise
- The other patch changes back the constness of phi. But this breaks other instantiations. The only one that affected swak was Su. But maybe others will have to be changed