def statement and define_method now return symbol a la Ruby2.1

src/class.c

@@ -1486,7 +1486,7 @@ mod_define_method(mrb_state *mrb, mrb_value self)
   mrb_proc_copy(p, mrb_proc_ptr(blk));
   p->flags |= MRB_PROC_STRICT;
   mrb_define_method_raw(mrb, c, mid, p);
-  return blk;
+  return mrb_symbol_value(mid);
 }
 
 static void

src/codegen.c

@@ -2317,7 +2317,7 @@ codegen(codegen_scope *s, node *tree, int val)
       pop();
       genop(s, MKOP_AB(OP_METHOD, cursp(), sym));
       if (val) {
-        genop(s, MKOP_A(OP_LOADNIL, cursp()));
+        genop(s, MKOP_ABx(OP_LOADSYM, cursp(), sym));
         push();
       }
     }
@@ -2337,7 +2337,7 @@ codegen(codegen_scope *s, node *tree, int val)
       pop();
       genop(s, MKOP_AB(OP_METHOD, cursp(), sym));
       if (val) {
-        genop(s, MKOP_A(OP_LOADNIL, cursp()));
+        genop(s, MKOP_ABx(OP_LOADSYM, cursp(), sym));
         push();
       }
     }