Refactor the samevalue internal method and add tests for this method.

Refactor the samevalue internal method and add tests for this method.

Noticing that the only difference between samevalue and strict equality is on
numbers we can simplify SameValue.

The old version did not return a correct answer if called on two strings since
StringEquals (from runtime.cc) returns an answer that is the negated value
(if treated as a boolean).

Review URL: http://codereview.chromium.org/2136024

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4713 ce2b1a6d-e550-0410-aec6-3dcde31c8c00