Let collectgarbage() behave as collectgarbage("collect")

README.html

@@ -971,6 +971,7 @@ Files are no longer hosted at LuaForge.
 <li>Fix string backing ownership issue when compiling many scripts.</li>
 <li>Make LuaC compile state explicit and improve factoring.</li>
 <li>Add sample build.gradle file for Android example.</li>
+<li>collectgarbage() now behaves same as collectgarbage("collect") (fixes issue #41).</li>
 
 </ul></td></tr>
 </table></td></tr></table>

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

@@ -134,7 +134,7 @@ public class BaseLib extends TwoArgFunction implements ResourceFinder {
 	// "collectgarbage", // ( opt [,arg] ) -> value
 	static final class collectgarbage extends VarArgFunction {
 		public Varargs invoke(Varargs args) {
-			String s = args.checkjstring(1);
+			String s = args.optjstring(1, "collect");
 			if ( "collect".equals(s) ) {
 				System.gc();
 				return ZERO;