Allow operator names as getters/setters

Fixes #919

Fix provided by @kzc

test/compress/issue-12.js

@@ -9,3 +9,50 @@ keep_name_of_setter: {
     input: { a = { set foo () {} } }
     expect: { a = { set foo () {} } }
 }
+
+setter_with_operator_keys: {
+    input: {
+        var tokenCodes  = {
+            get instanceof(){
+                return test0;
+            },
+            set instanceof(value){
+                test0 = value;
+            },
+            set typeof(value){
+                test1 = value;
+            },
+            get typeof(){
+                return test1;
+            },
+            set else(value){
+                test2 = value;
+            },
+            get else(){
+                return test2;
+            }
+        };
+    }
+    expect: {
+        var tokenCodes  = {
+            get instanceof(){
+                return test0;
+            },
+            set instanceof(value){
+                test0 = value;
+            },
+            set typeof(value){
+                test1 = value;
+            },
+            get typeof(){
+                return test1;
+            },
+            set else(value){
+                test2 = value;
+            },
+            get else(){
+                return test2;
+            }
+        };
+    }
+}