Bug:Strict mode write to indexed getter only prop should throw TypeError

There appears to be an error in strict mode detecting that a getter only property is read-only when that property is numerically indexed instead of having a name.

I would expect both of the below tests (1 and 2) to throw errors in strict mode, but with current CC master (and latests release) only the 2nd one does.
```js
"use strict";
const obj = { get "0" () { return 0; }, get bar () { return 0; }}
try { //test 1
obj[0] = 1;
print("expected error not thrown - attempted write to getter only obj[0]");
}
catch(e) {
print(e);
}

try { //test 2
obj.bar = 1;
print("expected error not thrown - attempted write to getter only obj.bar");
}
catch(e) {
print(e);
}
```

eshost output:
```
#### Chakra
expected error not thrown - attempted write to getter only obj[0]
TypeError: Assignment to read-only properties is not allowed in strict mode

#### V8 --harmony
TypeError: Cannot set property 0 of # which has only a getter
TypeError: Cannot set property bar of # which has only a getter

#### JavaScriptCore
TypeError: Attempted to assign to readonly property.
TypeError: Attempted to assign to readonly property.

#### SpiderMonkey
TypeError: setting getter-only property 0
TypeError: setting getter-only property "bar"
```

Reproduce the two strict-mode assignments from the issue, comparing the numeric key obj[0] with the named getter obj.bar. Trace the strict-mode assignment handling for indexed properties and add a regression test; done means both writes throw TypeError as shown by the other engines.

Written by the indexing model from the issue text.