JSHint plugin should populate Vim's location list instead of quick fix list

While linting a js file with JSHint, it makes more sense to use the location list instead of the quick fix window.

One scenario that illustrates this is when users grep for some pattern within their project files, using a different plugin that populates the quick fix list with results. When the quick fix window pops up, the user will select a result from the list and jump directly to that result in another file. If that file happens to be a javascript file, the JSHint plugin lints the file automatically once the buffer is fully read. This action overwrites the contents of the quick fix window that contained the grep results, forcing the user to grep again, which is inconvenient.

Using the location list for linting prevents interference with quick fix enhanced greping, and other actions that are concerned with listing locations from multiple files (compiling, etc.). Besides, when you are linting in an editor, you're usually only concerned with the contents of that particular file.