Reject NCNames when they might be part of an unexpected QName

[GuntherRademacher]

The "longest token rule" in A.3 Lexical structure states:

If the current position is not the end of the input, then return the longest literal terminal or variable terminal that can be matched starting at the current position, regardless whether this terminal is valid at this point in the grammar.

As a consequence, an NCName must not be accepted when it is followed by a colon and a name-start character, because in that case the input should be tokenized as a QName, even if only an NCName is expected by the grammar at that point.

This change marks NCName tokenization calls with a boolean that controls whether a following : plus name-start character is permitted, and rejects the token if it is not.

This fixes QT4 test case MapConstructor-025a.

[GuntherRademacher]

With this fix I have taken the more general route by addressing this on NCName level. A simpler version would just inspect the context following an NCName as a KeySpecifier - I believe that this is the only situation where a following colon plus name start, if not rejected, would be a continuation that might be part of an otherwise valid query. Please let me know if you prefer the simpler variant.

[ChristianGruen]

Looks good; thanks. One never knows what is going to happen next.