bug#12615: 24.2.50; Non-ignored case in insert-char

[Harald Hanche-Olsen <hanche@math.ntnu.no>]

Thinking about this on my way home from work, I think I figured out
the reason for this problem:

The let binding of completion-ignore-case takes place in the current
buffer, and so overrides the buffer-local binding. However, the
variable is used in the minibuffer, in which the buffer-local binding
(and with it, the let binding) is not visible; it uses the global
binding instead.

I am not totally sure about this; however, a simple experiment shows
that buffer-local bindings and let bindings interact in the way
described.

If I am right, then making completion-ignore-case buffer-local makes
no sense, as it can't have any effect. (If you're curious, mew does
this. I should contact the author to find out why.)

As to whether this is an emacs bug, I am no longer sure.

But I can't find anything in the elisp manual about how let operates
on buffer-local variables.

- Harald