bug#21578: `ibuffer-copy-filename-as-kill' unconsistent with `dired-copy-filename-as-kill'

[Tino Calancha]

This is not a bug, its a suggestion.

It would be pleasant if these two functions would behave similarly
whenever we dont have marked files: the later one returns filename for 
next ARG files (or file in the current line if ARG nil), which i found useful.
The former one report an error and exists.

I found better if `ibuffer-copy-filename-as-kill' behaves as the 
dired function in that situation.

Attached two patches:

*) one over emacs-v24.5 ibuf-ext.el
*) another including patches from bug reports #21576, #21577.

patch3
Description: Text document

patch4
Description: Text document