[RFC] vim-patch:7.4.279

```
Problem:    globpath() returns a string, making it difficult to get a
            list of matches.  (Greg Novack)
Solution:   Add an optional argument like with glob().  (Adnan Zafar)
```
https://code.google.com/p/vim/source/detail?r=8e9db1f27a0063df023cc05a760fce73255dad24\

Biggest difference between this and the original patch is that we already have `ga_concat_strings_sep()`, so I didn't feel the need to add the `sep` argument to `ga_concat_strings()`. However, I did feel the need to add `@param sep` to the doxy comment.
Typo of -> if

Why not use a similar comment above the the test for the third argument and remove this one?