delete all uses of panicln by rewriting them using panic or,
in the tests, println+panic.
gofmt some tests too.

R=rsc
CC=golang-dev
https://golang.org/cl/741041
diff --git a/src/pkg/net/fd.go b/src/pkg/net/fd.go
index df5a39d..5619b9e 100644
--- a/src/pkg/net/fd.go
+++ b/src/pkg/net/fd.go
@@ -128,7 +128,7 @@
 		return
 	}
 	if err := s.poll.AddFD(intfd, mode, false); err != nil {
-		panicln("pollServer AddFD ", intfd, ": ", err.String(), "\n")
+		panic("pollServer AddFD " + err.String())
 		return
 	}