Hammer out some char * vs unsigned char * problems. In general, I've kept

Hammer out some char * vs unsigned char * problems.  In general, I've kept
any buffers used internally by telnet.c as unsigned char, and cast to/from
char * when interacting with the rest of PuTTY.  Not actually tested, since
I'm some way from actually being able to link this yet.

Also clean up a couple of style warnings from Apple's compilers.

[originally from svn r2447]