importJSON function overwrites insert method in path with a variable.

[r03ert0]

Description/Steps to reproduce

Create an empty path, check whether path.insert is a function (as it should be). Now, import a path using path.importJSON(). path.insert should still be a function, however, it's now a boolean variable assigned the value false. This bug breaks in particular the possibility of running path.divideAt() on the imported path, or any other function that would require path.insert().

Expected result

After path.importJSON(), the function path.insert should still exist, however, it's replaced by a boolean variable.

Additional information

The culprit is this part in paperjs's code:

	importJSON: function(json, target) {
		return Base.deserialize(
				typeof json === 'string' ? JSON.parse(json) : json,
				function(ctor, args, isRoot) {
					var useTarget = isRoot && target
							&& target.constructor === ctor,
						obj = useTarget ? target
							: Base.create(ctor.prototype);
					if (args.length === 1 && obj instanceof Item
							&& (useTarget || !(obj instanceof Layer))) {
						var arg = args[0];
						if (Base.isPlainObject(arg))
							arg.insert = false;
					}
					(useTarget ? obj.set : ctor).apply(obj, args);
					if (useTarget)
						target = null;
					return obj;
				});
	},

arg.insert is overwriting the path.insert function. Replacing arg.insert = false by arg.insertFlag = false, solves the issue of the overwritten path.insert function. In particular, it is now possible to run path.divideAt().

Tested on Mac OS Sierra 10.12.6 (16G29), Chrome 57.0.2987.98 (64-bit).