let tor compile with tls on rh9

let tor compile with tls on rh9

nick: is this the right way to do the autoconf stuff? what happens when
/usr/kerberos/include/ doesn't exist?
an alternate way is to add `pkg-config --cflags openssl` to CFLAGS, but
it seems that command only works on rh9. yay portability issues.

svn:r453