More bulletproof util.inspect() function.

[TooTallNate]

Use the real versions of the Date and RegExp functions, from the
prototype. This defends against code like:

var d = new Date()
d.toUTCString = null
util.inspect(d)
  // TypeError: toUTCString is not a function

Or:

var r = /a regexp/
r.toString = null
util.inspect(r)
  // TypeError: Cannot convert object to primitive value

[TooTallNate]

Added test cases.

[koichik]

Thanks!