[RFC] stylistic globpath improvements

This is a fallow-up of  #1019 (patch [279](https://code.google.com/p/vim/source/detail?r=8e9db1f27a0063df023cc05a760fce73255dad24%5C)) I had some more controversial changes I wanted to make, but didn't want to obfuscate the review process or jeopardize the patch, so I left them out. 

See the comment at the bottom of  f33fad2c0bbd10dc8e19039c9de5b0588aca3c3b to view the diff, but ignoring whitespace.
Instead of duplicating the strings pointed to by `p`, we could just copy the pointers (`FreeWild` would free them anyway):
```c
    ga_grow(ga, num_p);
    for (int i = 0; i < num_p; i++) {
      GA_APPEND(char_u *, ga, p[i]);
    }
    free(p);  // no FreeWild anymore
```