Get rid of getStride()

It was confusing and not properly used everywhere.
Callers should use the stride they get when they get
the buffer pointer.
diff --git a/vncviewer/OSXPixelBuffer.cxx b/vncviewer/OSXPixelBuffer.cxx
index fc216a1..d196497 100644
--- a/vncviewer/OSXPixelBuffer.cxx
+++ b/vncviewer/OSXPixelBuffer.cxx
@@ -39,7 +39,7 @@
 OSXPixelBuffer::OSXPixelBuffer(int width, int height) :
   PlatformPixelBuffer(rfb::PixelFormat(32, 24, false, true,
                                        255, 255, 255, 16, 8, 0),
-                      width, height, NULL),
+                      width, height, NULL, width),
   bitmap(NULL)
 {
   CGColorSpaceRef lut;