BView: add methods for affine translation/scaling/rotation

* BView::TranslateBy(), BView::ScaleBy() and BView::RotateBy()
  allow to conveniently modify the current affine transformation.
  This makes it unnecessary to first read the current transform,
  modify it, and then set it again.
  Uses the new Pre...() methods of BAffineTransform.

* Also, remove setting the transform "through" to the BView even
  while recording a BPicture, as this now results in transforms
  being applied more than once.

headers/private/app/ServerProtocol.h

@@ -343,6 +343,10 @@ enum {
 	AS_VIEW_SET_TRANSFORM,
 	AS_VIEW_GET_TRANSFORM,
 
+	AS_VIEW_AFFINE_TRANSLATE,
+	AS_VIEW_AFFINE_SCALE,
+	AS_VIEW_AFFINE_ROTATE,
+
 	// Polygon filling rules
 	AS_VIEW_SET_FILL_RULE,
 	AS_VIEW_GET_FILL_RULE,