rename units -> units.txt.

add makefile rules to build a binary named units as a demo.

R=r
DELTA=1257  (659 added, 597 deleted, 1 changed)
OCL=34528
CL=34530

src/cmd/goyacc/Makefile

@@ -10,3 +10,8 @@ GOFILES=\
 
 include $(GOROOT)/src/Make.cmd
 
+units: goyacc units.y
+	goyacc units.y
+	$(GC) y.go
+	$(LD) -o units y.$O
+

src/cmd/goyacc/units.y

@@ -21,6 +21,8 @@
 //		/ 5.5474878e-13
 //	you have:
 
+package main
+
 import
 (
 	"flag";
@@ -294,7 +296,7 @@ main()
 
 	flag.Parse();
 
-	file = "units";
+	file = "units.txt";
 	if flag.NArg() > 0 {
 		file = flag.Arg(0);
 	}