[wxMac] Core Text Support added to trunk

[Stefan Csomor]

Hi

I've added an implementation to wxFont and wxGraphicsContext that uses 
the new Core Text Framework when running under 10.5, in order to get 
that you will have to compile under 10.5, the code is weak linked, so 
unless you also define 10.5 to be your MINIMAL system, it will still 
render using ATSU when running under 10.4

So please test text rendering / measuring code under 10.5 (when also 
compiled under 10.5) and report back problems you encounter.

Thanks,

Stefan