stop swipe from triggering after multitouch gesture

if after pinch/rotate, one finger touchends before the other, swipe is
incorrectly triggered because the last gesture is a single-touch
gesture. this checked for maximum pointers in gesture

Fixes #640
Ref #639
Ref #806
Closes #669

src/input.js

@@ -173,15 +173,18 @@ function computeInputData(manager, input) {
 
     computeDeltaXY(session, input);
     input.offsetDirection = getDirection(input.deltaX, input.deltaY);
-    
+
     var overallVelocity = getVelocity(input.deltaTime, input.deltaX, input.deltaY);
     input.overallVelocityX = overallVelocity.x;
     input.overallVelocityY = overallVelocity.y;
     input.overallVelocity = (abs(overallVelocity.x) > abs(overallVelocity.y)) ? overallVelocity.x : overallVelocity.y;
-    
+
     input.scale = firstMultiple ? getScale(firstMultiple.pointers, pointers) : 1;
     input.rotation = firstMultiple ? getRotation(firstMultiple.pointers, pointers) : 0;
 
+    input.maxPointers = !session.prevInput ? input.pointers.length : ((input.pointers.length >
+        session.prevInput.maxPointers) ? input.pointers.length : session.prevInput.maxPointers);
+
     computeIntervalInputData(session, input);
 
     // find the correct target