Show the shaper name in the debug message (#306)

src/hb-shape-plan.cc

diff --git a/src/hb-shape-plan.cc b/src/hb-shape-plan.cc
index 56e2ea5..87231fb 100644
--- a/src/hb-shape-plan.cc
+++ b/src/hb-shape-plan.cc
@@ -289,9 +289,10 @@
 		       unsigned int        num_features)
 {
   DEBUG_MSG_FUNC (SHAPE_PLAN, shape_plan,
-		  "num_features=%d shaper_func=%p",
+		  "num_features=%d shaper_func=%p, shaper_name=%s",
 		  num_features,
-		  shape_plan->shaper_func);
+		  shape_plan->shaper_func,
+		  shape_plan->shaper_name);
 
   if (unlikely (!buffer->len))
     return true;