Improve iolib test.

src/core/org/luaj/vm2/lib/IoLib.java

@@ -469,7 +469,7 @@ public class IoLib extends OneArgFunction {
 	private static Varargs iowrite(File f, Varargs args) throws IOException {
 		for ( int i=1, n=args.narg(); i<=n; i++ )
 			f.write( args.checkstring(i) );
-		return LuaValue.TRUE;
+		return f;
 	}
 
 	private Varargs ioread(File f, Varargs args) throws IOException {

test/lua/iolib.lua

@@ -5,6 +5,15 @@ print( 'platform', platform )
 -- 
 -- C version on Windows will add change \n into \r\n for text files at least
 -- 
+local tostr,files,nfiles = tostring,{},0
+tostring = function(x)
+	local s = tostr(x)
+	if s:sub(1,4) ~= 'file' then return s end
+	if files[s] then return files[s] end
+	files[s] = 'file.'..nfiles
+	nfiles = nfiles + 1
+	return files[s]
+end
 print( io ~= nil )
 print( io.open ~= nil )
 print( io.stdin ~= nil )