PR tree-optimization/18463
	* tree-chrec.c (chrec_convert): Return fold_converted chrec if
	converting it directly is not possible.
	(chrec_convert_aggressive): New function.
	* tree-chrec.h (chrec_convert_aggressive): Declare.
	* tree-scalar-evolution.c (instantiate_parameters_1, resolve_mixers):
	Fold chrec conversions aggressively if asked to.
	(instantiate_parameters): Modified because of changes in
	instantiate_parameters_1.

From-SVN: r104443