Fix custom elements attribute application, improve key checking

- Fix custom elements attribute application to acknowledge that not all
  custom elements operate purely based on attributes. (Plus, those
  blasted things are verbose as heck when you're working with them in
  raw form. It's also not that uncommon for functionality to be exposed
  via property and *not* attribute.)
- Don't memoize the normalized value when we 1. only use it once in each
  branch, and 2. only use it for a few special cases.
- Centralize the "has property key" code, so it's easier to tune and
  read. I also inlined a couple functions while I was at it since they
  were small and only used once.
- Actually test for how attributes are applied to raw DOM elements vs
  when we choose to use keys. When I first developed the patch, it
  silently worked, when I should've been breaking things.

render/tests/test-hyperscript.js

@@ -302,6 +302,63 @@ o.spec("hyperscript", function() {
 			o(vnode.attrs.className).equals("a b")
 		})
 	})
+	o.spec("custom element attrs", function() {
+		o("handles string attr", function() {
+			var vnode = m("custom-element", {a: "b"})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals("b")
+		})
+		o("handles falsy string attr", function() {
+			var vnode = m("custom-element", {a: ""})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals("")
+		})
+		o("handles number attr", function() {
+			var vnode = m("custom-element", {a: 1})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals(1)
+		})
+		o("handles falsy number attr", function() {
+			var vnode = m("custom-element", {a: 0})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals(0)
+		})
+		o("handles boolean attr", function() {
+			var vnode = m("custom-element", {a: true})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals(true)
+		})
+		o("handles falsy boolean attr", function() {
+			var vnode = m("custom-element", {a: false})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals(false)
+		})
+		o("handles only key in attrs", function() {
+			var vnode = m("custom-element", {key:"a"})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs).equals(null)
+			o(vnode.key).equals("a")
+		})
+		o("handles many attrs", function() {
+			var vnode = m("custom-element", {a: "b", c: "d"})
+
+			o(vnode.tag).equals("custom-element")
+			o(vnode.attrs.a).equals("b")
+			o(vnode.attrs.c).equals("d")
+		})
+		o("handles className attrs property", function() {
+			var vnode = m("custom-element", {className: "a"})
+
+			o(vnode.attrs.className).equals("a")
+		})
+	})
 	o.spec("children", function() {
 		o("handles string single child", function() {
 			var vnode = m("div", {}, ["a"])