intersect.m: Accept a "legacy" flag for Matlab compatibility. * NEWS: Announce change. * intersect.m: Add new calling form and explanation of "legacy" option to docstring. Allow up to 4 inputs in input validation. Check for "legacy" in input options and set variable optlegacy. Only use two-input form of sort or sortrows when number of outputs of intersect function is greater than 1. After calculation, change orientation of outputs as required based on optlegacy. Add BIST tests to test output orientation and values. * validsetargs.m: Modify to accept a variable number of option arguments as last input (varargin). Use switch statement to validate possible options including accepting "legacy".

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