Hi,

the case conversion in Emacs 22 makes large nnfolder groups very slow
if the user has a Turkish locale because of the Turkish case
conversion of `i' and `I' into `İ' and `ı'
(cf. `turkish-case-conversion-enable').

[ See
  http://thread.gmane.org/gmane.emacs.devel/68859/focus=64496
  http://thread.gmane.org/gmane.emacs.gnus.general/63925/focus=63979
  for more information. ]

The following patch should fix this slowness.  But I don't use
nnfolder myself and I don't have much time for testing, so I hesitate
to install it (even in the trunk).  Could someone please review the
patch and/or test it, please?

To change your locale to Turkish temporarily, you can start Emacs
using "LC_CTYPE=tr_TR emacs -f gnus".  But also testing it with your
usual locale if you are using nnfolder would be useful.