Use non-recursive version of file-seq

[skrat]

Fixes clojure-emacs/cider#1870

Do you need test for this? I wasn't quite sure how to write them. You can create a directory structure like:

foo/
  xxx/
    bar -> ../../bar (symlink)
bar/
  yyy/
    foo -> ../../foo (symlink)

Running (file-seq (File. "foo")) as compliment.utils/list-files does, will return an infinite sequence. Trying to consume it will likely lead to OOM.

[coveralls]

Coverage increased (+0.03%) to 97.188% when pulling c11fd5a on skrat:robust-list-files into 8d838df on alexander-yakushev:master.

[alexander-yakushev]

Yeah, setting up the test going to be messy. Let's merge it as is:) Thank you!