Fixes to parsing XSD dateTime values.

* [XSD_DATETIME,FIX] Removed a superfluous daysInMonth/3 check in dateTimeLexicalRep//1 (not in the standard, and clearly fails on valid arguments).
* [XSD_DATETIME,FIX] yearFrag//1 and secondFrag//1 used decimal digits where codes were required (since they are fed to another phrase/[2,3]).
* [XSD_DATETIME,FIX] in the XSD 1.1 standards, timeZoneFrag//1 uses unsignedDecimalPtNumeral//1 for parsing the minutes of the timezone offset. But the syntax shows that no decimal point is allowed here. Therefore, unsignedNoDecimalPtNumeral//1 suffices to assign the correct value to the timezone offset component. Moreover, since the decimal separator is REQUIRED by the syntactic rules for which unsingedDecimalPtNumeral//1 provides the semantics, we think it may also be incorrect to use this semantic rule here.
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