Deduplicate m.route and m.redraw logic (#2453)

- Remove appropriate route change subcriptions when a root is removed
  via `m.mount(root, null)`.
- Don't pollute `onpopstate` and friends - use standard event listeners
  instead.
- Simplify and streamline subscriptions, in preparation of adding a
  `remove` parameter to `m.mount`.
- Change the redraw internals to redraw immediately, with ability to
  cancel via returning a sentinel.
- Change `"bleeding-edge"` for `m.version` in `next` to instead just be
  the latest `m.version`. (If you're using `next`, you should know what
  you're in for.)
- Update tests to be aware of these changes. (Some were failing for
  subtle reasons.)
- Drive-by: remove some uses of `string.charAt(n)` and use `string[n]`
  instead.

api/mount.js

@@ -5,17 +5,11 @@ var Vnode = require("../render/vnode")
 module.exports = function(redrawService) {
 	return function(root, component) {
 		if (component === null) {
-			redrawService.render(root, [])
 			redrawService.unsubscribe(root)
-			return
+		} else if (component.view == null && typeof component !== "function") {
+			throw new Error("m.mount(element, component) expects a component, not a vnode")
+		} else {
+			redrawService.subscribe(root, function() { return Vnode(component) })
 		}
-		
-		if (component.view == null && typeof component !== "function") throw new Error("m.mount(element, component) expects a component, not a vnode")
-		
-		var run = function() {
-			redrawService.render(root, Vnode(component))
-		}
-		redrawService.subscribe(root, run)
-		run()
 	}
 }