bug#27518: 25.2.1; reftex-typekey-check seems to be case-insensitive

[Jörn Kommer]

It seems that, unexpectedly, ‘reftex-typekey-check’ is case-insensitive.
When I set ‘reftex-insert-label-flags’ for a key named ‘E’ to ‘nil t’,
these flags are also set for environments with the ‘e’ key (equations,
etc.).  As there are already the pre-defined labels ‘n (footnote)’ and ‘N
(endnote)’, and you're probably supposed to be able to set different
flags for them, this seems to be a bug.

As Andrew Swann (who found the bug in emacs.se:
https://emacs.stackexchange.com/q/33722/16178) pointed out, as a fix it
would probably be enough to set ‘case-fold-search’ to ‘nil’ locally, as
doing this globally seems to fix the issue.

As this is my first bug report, I hope I included everything important.  

Emacs  : GNU Emacs 25.2.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.22.10)
 of 2017-04-22
Package: 25.2.1

current state:
==============
(setq
 window-system 'x
 reftex-plug-into-AUCTeX t
 )