Improved and crossbrowser Array and Date type detection

isArray and isDate functionality is using so-called duck-typing to determine the type, it's very error-prone, so I suggest more error-proof and cross-browser implementation, that's actually even easier to read and to maintain.
More rationales in this popular article: http://perfectionkills.com/instanceof-considered-harmful-or-how-to-write-a-robust-isarray/.