test: use testlib (third 100)

X ,s;^// \$G (\$D/)?\$F\.go *$;// compile;g
X ,s;^// \$G (\$D/)?\$F\.go && \$L \$F\.\$A *$;// build;g
X ,s;^// \$G (\$D/)?\$F\.go && \$L \$F\.\$A && \./\$A\.out *$;// run;g
X ,s;^// errchk \$G( -e)? (\$D/)?\$F\.go *$;// errorcheck;g

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5656083

test/fixedbugs/bug381.go

@@ -1,4 +1,4 @@
-// errchk $G $D/$F.go
+// errorcheck
 
 // Copyright 2011 The Go Authors.  All rights reserved.
 // Use of this source code is governed by a BSD-style