- fixed 3134449 -- Date.UTC returns NaN (invalid date)

	Did more testing of the date functions and made them behave like the other browsers.
	There were three problems:

            1) We did a validity check that other browsers don't do (hence the NaN).
            2) We treated passed-in dates as local time even in Date.UTC (hence a wrong result
               once I fixed the NaN).
            3) The results of ToUTCString (and ToGMTString) weren't formatted quite the same
	       as other browsers.

	Also found a couple of silly but unrelated coding mistakes.

        * kjs/date_object.cpp:
        (timetUsingCF): Added. Has the guts of mktimeUsingCF, but without the CFGregorianDateIsValid
        check. Other browsers accept invalid dates. Also takes a time zone parameter.
        (mktimeUsingCF): Calls timetUsingCF with the current time zone.
        (timegmUsingCF): Calls timetUsingCF with the UTC time zone.
        (formatDate): Remove the includeComma flag.
        (formatDateUTCVariant): Added. For use instead of formatDate with the includeComma flag.
	Puts the day before the month name.
        (DateProtoFuncImp::call): Use the new formatDateUTCVariant for ToGMTString and ToUTCString.
	Without this change the date didn't match other browsers.
        (DateObjectImp::DateObjectImp): Use UTCPropertyName. Somehow I declared this and didn't use
	it before.
        (DateObjectImp::construct): Pass -1 for is_dst literally instead of using invalidDate.
	Changing this to invalidDate was just a mistake (although no real difference in compiled
	code since invalidDate is just -1).
        (DateObjectFuncImp::call): Call timegm for the UTC case instead of mktime.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@3177 268f45cc-cd09-0410-ab3c-d52691b4dbfc