cw3: Add alu_s_do to op process sensitivity list
cw3: ALU instruction fix ups
cw3: Implement ALU carry out
cw3: Only assign alu_[ab]_di when required
cw3: Implement comparison instructions
cw3: Update view
cw3: Implement signed comparisons
cw3: Fix ALU variable assignment
cw3: Fix ALU signed carry out assignment