Make date parser handle all ES5 Date Time Strings correctly.

This means that ES5 Date Time Strings will default to UTC if timezone is absent.
Handle as many legacy strings as possible the same way as before

BUG=v8:1498
TEST=mjsunit/date

Review URL: http://codereview.chromium.org/7291022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8513 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
6 files changed