re PR middle-end/19331 (Inefficient code generated for bitfield assignment)

	PR middle-end/19331
	* tree.c (get_unwidened): Treat CONVERT_EXPR and NOP_EXPR identically.
	* fold-const.c (fold_sign_changed_comparison): Likewise.
	(fold_binary): Optimize comparisons against widened operands if
	the extension is represented by a CONVERT_EXPR, same as a NOP_EXPR.

From-SVN: r96397