- fix http://bugs.webkit.org/show_bug.cgi?id=12867
          REGRESSION: BenchJS test 7 (dates) is 220% slower than in Safari 2.0.4

        * kjs/DateMath.h: Marked GregorianDateTime as noncopyable, since it has a non-trivial
        destructor and not the correspoding copy constructor or assignment operator.
        Changed the GregorianDateTime constructor to use member initialization syntax.
        Fixed the destructor to use the array delete operator, since timeZone is an array.

        * kjs/DateMath.cpp:
        (KJS::daysInYear): Changed to call isLeapYear so the rule is not repeated twice.
        (KJS::getUTCOffset): Added caching on PLATFORM(DARWIN), since we can rely on the
        notify_check function and "com.apple.system.timezone" to let us know when the
        offset has changed.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@19943 268f45cc-cd09-0410-ab3c-d52691b4dbfc