parameter to iconv()
(See http://lists.debian.org/debian-glibc/2004/05/msg00006.html)

I'm casting in the general case, but I added a non-const codepath in
case it matters on some platform.

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402386