Make nonexistent parent dirs in counsel-find-file-mkdir-action

[dmringo]

Currently if you dispatch the mkdir action from counsel-find-file with input (ivy-text, I think?) "multi/level/dirs", it will fail in make-directory because "multi" (relative to the default directory) doesn't exist. I think the intent in such a case would to make the all the directories and this change enables that by passing a non-nil optional argument PARENTS to make-directory.

Since this is such a small change, I don't think I need to worry about the copyright assignment and there doesn't seem to be any difference between my branch and master for the make checks.

I have an ERT test I can add too, but it feels a little weird since it involves modifying the filesystem and then cleaning up the changes.

[abo-abo]

Thanks.