Switch to using float for point size in wxNativeFontInfo

Use float as the fundamental type for the font size and implement
wxNativeFontInfo::{Set,Get}PointSize() as wrappers around the new
{Set,Get}FractionalPointSize().

Update wxNativeFontInfo for all platforms and replace the use of its
SetPointSize() method with SetFractionalPointSize() in wxFont for the
platforms already supporting fractional point sizes (don't change the
others just yet).

Note that wxNativeFontInfo::{Get,Set}PointSize() are preserved for
backwards compatibility but shouldn't be used in any code inside the
library itself any more (again, this is not the case yet, but will be
soon).

include/wx/fontutil.h

@@ -185,7 +185,7 @@ public :
     //
     #define wxNO_NATIVE_FONTINFO
 
-    int           pointSize;
+    float         pointSize;
     wxFontFamily  family;
     wxFontStyle   style;
     wxFontWeight  weight;
@@ -236,9 +236,9 @@ public:
         if ( font.IsUsingSizeInPixels() )
             SetPixelSize(font.GetPixelSize());
         else
-            SetPointSize(font.GetPointSize());
+            SetFractionalPointSize(font.GetFractionalPointSize());
 #else
-        SetPointSize(font.GetPointSize());
+        SetFractionalPointSize(font.GetFractionalPointSize());
 #endif
 
         // set the family/facename
@@ -268,7 +268,8 @@ public:
     wxFontFamily GetFamily() const;
     wxFontEncoding GetEncoding() const;
 
-    void SetPointSize(float pointsize);
+    void SetPointSize(int pointsize);
+    void SetFractionalPointSize(float pointsize);
     void SetPixelSize(const wxSize& pixelSize);
     void SetStyle(wxFontStyle style);
     void SetNumericWeight(int weight);