Never pass a `char' to a ctype function. I had relied on gcc -Wall

Never pass a `char' to a ctype function. I had relied on gcc -Wall
letting me know about instances of this, but it turns out that my
ctype.h explicitly casts input values to `int' to evade the
`subscript has type char' warning, so it had been carefully not
letting me know! Found them all by compiling with a doctored
ctype.h, and hopefully fixed them all too.

git-svn-id: svn://svn.tartarus.org/sgt/putty@2927 cda61777-01e9-0310-a592-d414129be87e