Don't rely on {}.toString() in old browsers (IE<=8)

[oleg8sh]

As you know, toString() method called on null returns "[object Null]", and on undefined returns "[object Undefined]".
But this is true for ECMAScript 5.1 and above.

Older browsers in both cases returns window.toString() that is "[object Object]".

So m("br") fails in IE8 when it tries to get hasAttrs variable value.

The same troubles can be found in build() if cached is undefined.

More info: http://tobyho.com/2011/01/28/checking-types-in-javascript/

P.S.: Changes in line 37 "... cached === null || cached === undefined ..." is also an alternative solution of #162
( #162 )

[pygy]

The thing is... instanceof has its own issues.

In the first case, we could check if args.length > 1.

Beside that check, the only change required is this line.

data can't be problematic thanks to this line, and the case where cached is null or undefined is covered by your check.

The third case benign.

[oleg8sh]

@pygy, You're absolutely right about instanceof.
This is named a "Cross-window Issues of instanceof" in the article from the first link.
And now I see @lhorie cleans out them from the next branch.

But {}.toString() has same issue for popups in IE, as mentioned in that article also.
So there is no easy way to satisfy any case.

PS: small useful change from this patch is extracted to #189.

[pygy]

On this topic, I'm currently pushing for the inclusion of a correct Object.prototype.toString in ES5Shim and polyfill.io so that we can rely completely on it.

es-shims/es5-shim#304
polyfillpolyfill/polyfill-service#401