bug#16548: 24.3; remove "buffer has clients" prompt

[Jarek Czekalski <jarekczek@poczta.onet.pl>]

When we try to kill a buffer, that was opened through
emacsclient, Emacs warns us: "buffer still has clients".
If we want to really kill it, we must answer "yes" (3 letters plus return).
If we modified the buffer, then in total we have 2 prompts to answer.
That seems too much and in help-gnu-emacs [1] no one could
provide a justification for that, other users seemed to
agree is is redundant. Eli had had some doubts, but
probably he got rid of them.

I suggest to remove the "buffer has clients" prompt completely.
If the buffer was not modified, it would close at once.

I want to prepare a patch, but may it be applied for 24.4,
despite feature freeze?

Jarek

[1] http://lists.gnu.org/archive/html/help-gnu-emacs/2013-11/msg00382.html