[Core] Workaround qmlRegisterTypeNotAvailable unavailability.

What an irony, qmlRegisterTypeNotAvailable is unavailable due to wrong
export macro.

There is a patch for Qt [1], but seems like it isn't incorporated anywhere,
so I better make a workaround.

[1] https://qt.gitorious.org/qt/cmarcelos-qtdeclarative/commit/522f0f92efcb1055081ab408c290d0452e4c6a14