[qtdeclarative] Ensure the vertical text alignment is updated when the Text height changes

Upstream change:
https://qt.gitorious.org/qt/qtdeclarative/commit/53bdf7daa1c598082dfde8bfbf40709f37f866e6
Merge pull request #58 from martinjones/text_valign

[qtdeclarative] Ensure the vertical text alignment is updated when the T...