Remove tuples before determining entity usage.
Remove tuples before determining entity usage.

Some optimizations, e.g., inlining, can create tuples with tuples as
operands.  The current code in determine_entity_usage cannot deal with
this situation and computes wrong usage information.  For now, we just
remove tuples before analysis.

MatzeB/libfirm,libfirm/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm