[trunk] Right-click Text Properties dlg box does not keep "Size follows space unit" setting

Setup: trunk rev. 4186 both under Win XP and Ubuntu 9.10

Steps:

1) Open (or create) a score with a staff text element (this probably applies also to other kinds of text elements)
2) Right-click the text element and choose "Test properties..."
3) If the text is "Style", change it to "Unstyled"
4) in the "Text Properties" dlg box, change the "size follows Space unit" setting
5) OK to close the dialogue box
6) Right-click the text element and choose "Test properties..." again

Result: the "size follows Space unit" setting changed in step 4) reverted to its original value

Note: The attached patch corrects the issue by adding two statements to function void Text::propertyAction() in file text.xpp (line 1204) which update the style sizeIsSpatiumDependent parameter if changed.