[QScintilla] wrong cursor moving

[petr at scribus.info]

ok, things moved quickly.

> I tested it on various OSes too - except windows. So here is the result:
> 
> http://bugreports.qt.nokia.com/browse/QTBUG-15039

after discussion with qt guys they suggested to use QFontMetricsF which
returns more precise results for find width - yes, mac uses non-int
sizes. This change should not have a performance affect (they said).

So I implemented a qscintilla patch (against 2.4.5):

http://pastie.org/1274576

It works on mac with all font types (fixed/variable widths and various
sizes). Apps using qscintilla don't look ugly now and can be used.

Let me know, if the patch can be accepted or if I should rewrite it -
eg. to use QFontMetricsF only for Q_WS_MAC etc.

cheers,
petr