Optimize selecting font in generated PostScript code

Emit code to select PostScript font only if it is needed (not at every call to SetFont(), but only if font has been really changed prior to a text drawing operation).

include/wx/generic/dcpsg.h

@@ -139,6 +139,8 @@ protected:
 
     // Common part of DoDrawText() and DoDrawRotatedText()
     void DrawAnyText(const wxWX2MBbuf& textbuf, wxCoord testDescent, double lineHeight);
+    // Actually set PostScript font
+    void SetPSFont();
 
     FILE*             m_pstream;    // PostScript output stream
     unsigned char     m_currentRed;
@@ -151,6 +153,7 @@ protected:
     wxPrintData       m_printData;
     double            m_pageHeight;
     wxArrayString     m_definedPSFonts;
+    bool              m_isFontChanged;
 
 private:
     wxDECLARE_DYNAMIC_CLASS(wxPostScriptDCImpl);