bug#20687: 25.0.50; `perform-replace' should invoke a key that you have bound in `query-replace-map'

[Drew Adams <drew.adams@oracle.com>]

> Could you please send an example of your custom keybindings in
> `query-replace-map' that currently don't work.

I don't have any custom keybindings in `query-replace-map' that
don't work (in fact, I don't have any custom bindings in that
map at all).

This bug report came from this emacs.StackExchange answer - see
the discussion in the comments.
http://emacs.stackexchange.com/a/12781/105.

The aim here was to add `C' to `query-replace-map', to have it
toggle `case-fold-search'.  But it doesn't matter what key a
user might want to bind to what command during q-r.

The point is that a user can do that (that's what keymaps and
key bindings are for), but currently `perform-replace' refuses to
recognize such a key and its command.

There is no good reason for this, AFAICT.  It should be OK for
a user to do this.  Of course, that doesn't update the doc
string to reflect the new key and its action, but that's all.
At the user level, this should be something that users can do
easily, without needing to perform surgery.