get_copy_remotes() to take ref of annex output

Output of 'git-annex whatis' calls is now passed to get_copy_remotes()
as a reference to the array instead of copying it.
get_annex_output() returns a ref to output array

The main logic dealing with the output now uses references all the time.
Remove trailing / from target dir

Fixes a bug where if the target was a dir, an extra slash would remain
in all fragile file printouts.