Fixed path problem in windows

Summary:

- `$file->getPathName()` may return a path like `C:\Somepath\To\The/Project`; so use `getRealpath` to return a normalized path.

- `str_replace` all `'\\'` into `'/'`

- `strrpos`, should we search from the reverse side? because if I am using it as standalone and the project name starts with `ClassPreloader` then the `strpos($filename, '/ClassPreloader/')` will return a wrong position.