Fix typed array check in Safari

Unfortunately, in Safari `typeof Uint8Array` and `typeof ArrayBuffer` return `'object'` instead of `'function'`, so typed arrays were not being used there. We can check `Uint8Array.constructor` to see if its a function cross browser, but we'd also have to check for null and undefined first. I think it's easier just to try constructing one in the try..catch block that is already there.
Merge branch 'patch-1' of github.com:devongovett/buffer into devongovett-patch-1