Set part.angle in Body.update.

[kenrose]

This change fixes a discrepency between Body.setAngle and Body.update.

Calling part.angle should always return the world space angle of the part.

In Body.setAngle, part.angle is correctly updated for every part. This maintains the invariant.

In Body.update, part.angle was previously not being updated. This led to stale values returned for part.angle.

Here's an example demonstrating that behaviour (paste into examples/):

(function() {

    var World = Matter.World,
        Bodies = Matter.Bodies,
        Body = Matter.Body,
        Common = Matter.Common,
        Events = Matter.Events;

    Example.angleSetting = function(demo) {
        var engine = demo.engine,
            world = engine.world;

        function inDegrees(radians) {
            return radians * (180.0 / Math.PI);
        }

        function inRadians(degrees) {
            return degrees * (Math.PI / 180.0);
        }

        function createBodyWithParts(x, y) {
            var width = 200;
            var height = 100;

            var outer = Bodies.rectangle(x, y, width, height);
            var inner = Bodies.rectangle(x, y + height / 2, width / 5, height / 5);
            Body.setAngle(inner, inRadians(30));
            return Body.create({parts: [outer, inner]});
        }

        function getInnerPart(body) {
            return body.parts[body.parts.length - 1];
        }

        var bodies = [
            createBodyWithParts(200, 200),
            createBodyWithParts(500, 200)
        ];

        // Use setAngle for one body
        Body.setAngle(bodies[0], inRadians(45));

        // Apply some angular acceleration on the other body
        Body.setAngularVelocity(bodies[1], 0.05);

        world.gravity = {x: 0.0, y: 0.0};
        World.add(world, bodies);

        var timeout = 5000; // ms
        window.setTimeout(function() {
            bodies.forEach(function(body) {
                var part = getInnerPart(body);
                console.log('body id ', body.id, ' has angle ', inDegrees(part.angle));
            });
        }, timeout);
    };
})();

[kenrose]

Any update on merging this PR?