Update the uggrid undefs!

While compiling a larger project, I faced a compiler error in AlbertaReader, that is somehow triggered by a macro undef in ug_undefs.hh. There, the macro DIM_MAX is undefined. For some reasons this is in conflict with the macro DIM_MAX in alberta/alberta.h. I have not fully understood the problem, but the c-preprocessor does not expand this macro anymore. The solution was to reorder my includes and first include albertagrid.hh and then uggrid.hh.

See the attached minimal example to reproduce the error. uggrid_error.cc

My suggestions is to update the undefs in ug_undefs.hh. I think, it is not required to undefine DIM_MAX since this macro is not used inside dune-uggrid anywhere, but I might be wrong.