Add test for combination of print() and tostring(), test case when tostring is changed in global environment.

src/core/org/luaj/lib/BaseLib.java

@@ -122,10 +122,17 @@ public class BaseLib extends LFunction {
 		switch ( id ) {
 		case PRINT: {
 			int n = vm.gettop();
+			vm.getglobal("tostring");			
 			for ( int i=2; i<=n; i++ ) {
+				vm.pushvalue(-1);
+				vm.pushvalue(i);
+				vm.call(1, 1);
+				if ( vm.type(-1) != Lua.LUA_TSTRING )
+					vm.error( "'tostring' must return a string to 'print'" );				
 				if ( i > 2 )
 					STDOUT.print( "\t" );
-				STDOUT.print( vm.tostring(i) );
+				STDOUT.print( vm.tostring(-1) );
+				vm.poplvalue();
 			}
 			STDOUT.println();
 			vm.resettop();

src/core/org/luaj/vm/LValue.java

@@ -321,7 +321,10 @@ public class LValue {
 		baos.write(b,0,b.length);
 	}
 
-	/** Return true if this is a LString */
+	/** Return true if this is a lua string, meaning it is 
+	 * either a LString or LNumber,since all numbers are 
+	 * convertible to strings in lua
+	 */
 	public boolean isString() {
 		return false;
 	}

src/test/java/org/luaj/vm/CompatibiltyTest.java

@@ -112,6 +112,10 @@ public class CompatibiltyTest extends ScriptDrivenTest {
 		runTest("pcalls");
 	}
 
+	public void testPrint() throws IOException, InterruptedException {
+		runTest("print");
+	}
+
 	public void testRequire() throws IOException, InterruptedException {
 		runTest("require");
 	}

src/test/res/print.lua

@@ -0,0 +1,26 @@
+-- print uses tostring under-the-hood!
+
+local function f()
+	print()
+	print('abc')
+	print(123)
+	print(true)
+	print('abc',123,true)
+end
+
+local function g()	
+	local fenv = {tostring=function(x)
+		return '*'..type(x)..'*'
+	end}
+	package.seeall(fenv)	
+	f()
+	print('setfenv', pcall(setfenv, 0, fenv), {}, f )
+	f()
+end
+
+local s,c = pcall( coroutine.create, g )
+print('create', s, s and type(c) or c)
+print('resume', pcall( coroutine.resume, c ) )
+f()
+
+