rust-needsdrop: simplify check_drops now dataflow itself computes intersection.
root testsuite: Update foo19 to reflect separate-but-equal arms.
root testsuite: Address a number of warnings to ease reading output.
root testsuite: Updated foo*.rs to be robust against new scope-end fwd-scan.
root testsuite: Some generalization to make clear the distinction i am drawing
between a return statement and the final expression.
rust-needsdrop: checkpoint scope-end fwd-scan semi-hack.