Workaround bug in node ~0.6.21 where native forEach doesn't box 3rd parameter.
Fix test case for Date.prototype.valueOf().

This test case failed when run in a UTC timezone, because 0 is not truthy.
Use a more precise test for an integer value.

Fixes #181.
Adding semicolons to the beginning of the shim files to prevent concatenation errors.
Added comment next to semicolon to explain their presence.