Change cursor API to use RGBA data

This will allow us to use better formats that preserve the entire
alpha channel.
diff --git a/tests/encperf.cxx b/tests/encperf.cxx
index d58d82e..7b9ff81 100644
--- a/tests/encperf.cxx
+++ b/tests/encperf.cxx
@@ -90,7 +90,7 @@
                 unsigned long long& rawEquivalent);
 
   virtual void setDesktopSize(int w, int h);
-  virtual void setCursor(int, int, const rfb::Point&, void*, void*);
+  virtual void setCursor(int, int, const rfb::Point&, const rdr::U8*);
   virtual void framebufferUpdateStart();
   virtual void framebufferUpdateEnd();
   virtual void dataRect(const rfb::Rect&, int);
@@ -207,7 +207,7 @@
   setFramebuffer(pb);
 }
 
-void CConn::setCursor(int, int, const rfb::Point&, void*, void*)
+void CConn::setCursor(int, int, const rfb::Point&, const rdr::U8*)
 {
 }