bug#21578: `ibuffer-copy-buffername-as-kill'

[Tino Calancha]

I also miss a function like:
ibuffer-copy-buffername-as-kill

Sometimes you want the buffer name at the current line regardless
of whether this buffer is visiting a file or not.
I would like this function behave similarly as
ibuffer-copy-filename-as-kill concerning with if we have marked buffers
or not.

In principle, such function could be bind to "B".
In my case i bind it to "b" (re-binding `ibuffer-bury-buffer'
to "B", because i rarely use this function).