all: use "reports whether" in place of "returns true if(f)"

Comment changes only.

Change-Id: I56848814564c4aa0988b451df18bebdfc88d6d94
Reviewed-on: https://go-review.googlesource.com/7721
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index 9db5faf..b6f4374 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -646,7 +646,7 @@
 		externalthreadhandlerp != 0 && pc == externalthreadhandlerp
 }
 
-// isSystemGoroutine returns true if the goroutine g must be omitted in
+// isSystemGoroutine reports whether the goroutine g must be omitted in
 // stack dumps and deadlock detector.
 func isSystemGoroutine(gp *g) bool {
 	pc := gp.startpc