bug#14340: Acknowledgement (24.3.50; Case insensitivity with read-file-name)

[Harald Hanche-Olsen]

Upon further reflection (in the bath), I think I understand the nature
of the bug, if not its resolution:

read-file-name-default let binds completion-ignore-case to the value of
read-file-name-completion-ignore-case before doing a pile of setup
work and calling completing-read.

When completion-ignore-case is buffer local, let overrides the buffer
local binding and not the global binding. But because completing-read
evaluates the variable in the minibuffer, it gets the global value
instead, i.e., nil.

(I may be wrong about some details in this, but I but this is the gist
of the problem.)

- Harald