Cache Gregorian date/time structure on DateInstance objects for 1.027x SunSpider speedup
        (1.65x on date-format-xparb, 1.13x on date-format-tofte).

        * kjs/DateMath.h:
        (KJS::GregorianDateTime::copyFrom): Added. It presumably makes sense to keep GregorianDateTime
        Noncopiable, so it's not just operator=.

        * kjs/date_object.h: Added a per-object cache.

        * kjs/date_object.cpp:
        (KJS::DateInstance::DateInstance):
        (KJS::DateInstance::msToGregorianDateTime):
        (KJS::dateProtoFuncToString):
        (KJS::dateProtoFuncToUTCString):
        (KJS::dateProtoFuncToDateString):
        (KJS::dateProtoFuncToTimeString):
        (KJS::dateProtoFuncToLocaleString):
        (KJS::dateProtoFuncToLocaleDateString):
        (KJS::dateProtoFuncToLocaleTimeString):
        (KJS::dateProtoFuncGetFullYear):
        (KJS::dateProtoFuncGetUTCFullYear):
        (KJS::dateProtoFuncToGMTString):
        (KJS::dateProtoFuncGetMonth):
        (KJS::dateProtoFuncGetUTCMonth):
        (KJS::dateProtoFuncGetDate):
        (KJS::dateProtoFuncGetUTCDate):
        (KJS::dateProtoFuncGetDay):
        (KJS::dateProtoFuncGetUTCDay):
        (KJS::dateProtoFuncGetHours):
        (KJS::dateProtoFuncGetUTCHours):
        (KJS::dateProtoFuncGetMinutes):
        (KJS::dateProtoFuncGetUTCMinutes):
        (KJS::dateProtoFuncGetSeconds):
        (KJS::dateProtoFuncGetUTCSeconds):
        (KJS::dateProtoFuncGetTimezoneOffset):
        (KJS::setNewValueFromTimeArgs):
        (KJS::setNewValueFromDateArgs):
        (KJS::dateProtoFuncSetYear):
        (KJS::dateProtoFuncGetYear):
        Use the cache when converting.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31937 268f45cc-cd09-0410-ab3c-d52691b4dbfc