Improving the robustness of zoom a lot!

Before, logic for recognizing zoom start was inconsistent between:
- *one* touchstart event w/ *two* fingers, vs.
- *two* touchstart events w/ *one* finger each.
Now, the logic is consistent; the same event handlers are added, etc.

Before, if the only touchmove events were with two fingers down, they were
ignored completely, so the touchend handler would reset x and y, assuming no
movement happened. Now, we properly recognize zoom and don't reset then.

Together, these almost entirely (but not quite, argh!) eliminate the annoying
bug where at the end of a pinch zoom, the content snaps to the top-left.
Overall, though, the entire zooming experience is *much* better now.

src/iscroll.js

@@ -329,22 +329,11 @@ iScroll.prototype = {
 			matrix;
 
 		that.moved = false;
+		that.zoomed = false;
+		    // TEMP aseemk: keep track of whether a zoom took place also.
 
 		e.preventDefault();
 
-		if (e.touches && e.touches.length == 2 && that.options.zoom && hasGesture) {
-			// As object position might change over time, we calculate the offset each time (overkill?)
-			el = that.wrapper;
-			do {
-				offsetLeft += el.offsetLeft;
-				offsetTop += el.offsetTop;
-			} while (el = el.offsetParent);
-
-			that.originX = abs(e.touches[0].pageX + e.touches[1].pageX - offsetLeft*2) / 2 - that.x;
-			that.originY = abs(e.touches[0].pageY + e.touches[1].pageY - offsetTop*2) / 2 - that.y;
-			return;
-		}
-
 		that.moved = false;
 		that.distX = 0;
 		that.distY = 0;
@@ -379,10 +368,31 @@ iScroll.prototype = {
 		that.bind(MOVE_EV);
 		that.bind(END_EV);
 		that.bind(CANCEL_EV);
+
+		// TEMP aseemk: setting zoom calculations *after* event listeners have been bound.
+		// remember that a multi-touch can begin both via *one* touchstart (with 2 touches)
+		// or via *two* touchstarts (first with 1 touch, second with 2 touches). we want to
+		// be consistent in both cases, i.e. setting the same properties, etc.
+
+		if (e.touches && e.touches.length >= 2 && that.options.zoom && hasGesture) {
+			// As object position might change over time, we calculate the offset each time (overkill?)
+			el = that.wrapper;
+			do {
+				offsetLeft += el.offsetLeft;
+				offsetTop += el.offsetTop;
+			} while (el = el.offsetParent);
+
+			that.originX = abs(e.touches[0].pageX + e.touches[1].pageX - offsetLeft*2) / 2 - that.x;
+			that.originY = abs(e.touches[0].pageY + e.touches[1].pageY - offsetTop*2) / 2 - that.y;
+		}
 	},
 
 	_move: function (e) {
-		if (e.touches && e.touches.length > 1) return;
+	    if (e.touches && e.touches.length > 1) {
+	        // TEMP aseemk: remember that zooming happened
+	        this.zoomed = true;
+	        return;
+	    }
 
 		var that = this,
 			point = hasTouch ? e.changedTouches[0] : e,
@@ -457,7 +467,7 @@ iScroll.prototype = {
 	},
 
 	_end: function (e) {
-		if (e.touches && e.touches.length != 0) return;
+	    if (e.touches && e.touches.length > 0) return;
 
 		var that = this,
 			point = hasTouch ? e.changedTouches[0] : e,
@@ -473,8 +483,22 @@ iScroll.prototype = {
 		that.unbind(MOVE_EV);
 		that.unbind(END_EV);
 		that.unbind(CANCEL_EV);
-
-		if (!that.moved) {
+
+		// TEMP aseemk: short-circuiting touchend calculations -- including momentum --
+		// if this was at all a multi-touch interaction. this is suboptimal because the
+		// user can start panning (single-touch) after zooming (multi-touch), which
+		// should use momentum, etc., but that calculation is broken -- it doesn't
+		// properly track fingers, which can change between start and end. note that
+		// unfortunately this also prevents clamping if panned beyond the boundaries.
+		// TODO track individual fingers so we can calculate momentum correctly for
+		// flicks after multi-touch pinch zooms, and also clamp/bounce on release.
+		if (that.zoomed) {
+		    return;
+		}
+
+		// TEMP aseemk: if we fix momentum for post-multi-touch and remove the
+		// short-circuit above, we still shouldn't execute this block if zoomed.
+		if (!that.moved && !that.zoomed) {
 			if (hasTouch) {
 				if (that.doubleTapTimer && that.options.zoom) {
 					// Double tapped