qdoc: Documentation for QMetaObject::Connection now appears

qdoc's faux C++ parser did not recognize class declarations
of the form:

class Name1::Name2 {
...
};

...where class Name2 is nested in class Name1. Now it does,
but this fix doesn't handle deeper nestings. doc needs a
proper C++ parser.

Task-number: QTBUG-28664
Change-Id: I5adf88cc1b2ce03f5565250734416bf9592914b5
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>