pbxProject.prototype.addToHeaderSearchPaths #13 issue, still appeared.

```
if (!buildSettings['HEADER_SEARCH_PATHS']) {
buildSettings['HEADER_SEARCH_PATHS'] = [INHERITED];
}
```

This can be changed like this?
```
if (!buildSettings['HEADER_SEARCH_PATHS']
|| buildSettings['HEADER_SEARCH_PATHS'] === INHERITED) {
buildSettings['HEADER_SEARCH_PATHS'] = [INHERITED];
}
```

从 pbxProject.prototype.addToHeaderSearchPaths 开始，检查 HEADER_SEARCH_PATHS 等于 INHERITED 时是如何处理的。将当前条件与提议的更改进行比较，然后使用 repository 中现有的检查来验证此情况是否会生成预期的头文件搜索路径。

由索引模型根据 Issue 内容生成。