Prevent double-inclusion of ssh.h in case of -DNO_SECURITY.

winshare.c includes ssh.h, but if you defined NO_SECURITY it then
decides to fall back to including the stub noshare.c, which includes
ssh.h again. Fix by moving a block of includes inside the ifdef.


git-svn-id: svn://svn.tartarus.org/sgt/putty@10184 cda61777-01e9-0310-a592-d414129be87e