(const_binop): Rework to only make constants in one place; always use size_int if...

(const_binop): Rework to only make constants in one place; always use size_int if small enough and of sizetype.

(const_binop): Rework to only make constants in
one place; always use size_int if small enough and of sizetype.
(size_int): Call force_fit_type.
(fold): Avoid ever changing type of input tree.

From-SVN: r13377