Import various range-op fixes from ranger branch.

Import various range-op fixes from ranger branch.

This patch imports three fixes from the ranger branch:

1. Fold division by zero into varying instead of undefined.
This provides compatibility with existing stuff on trunk.

2. Solver changes for lshift.
This should not affect anything on trunk, as it only involves
the GORI solver which is yet to be contributed.

3. Preserve existing behavior for ABS([-MIN,-MIN]).
This is actually unrepresentable, but trunk has traditionally
treated this as [-MIN,-MIN] so this patch just syncs range-ops
with the rest of trunk.

gcc/ChangeLog:

	* range-op.cc (operator_div::wi_fold): Return varying for
	division by zero.
	(class operator_rshift): Move class up.
	(operator_abs::wi_fold): Return [-MIN,-MIN] for ABS([-MIN,-MIN]).
	(operator_tests): Adjust tests.