Now that Halibut is capable of generating man pages better than I

Now that Halibut is capable of generating man pages better than I
can do it by hand, I've converted the man page set from Unix PuTTY
into Halibut format, and enhanced the Makefile so it will build
them. At some future point this will also allow me to include the
man pages as an appendix in the main manual (once I _have_ a main
manual for Unix PuTTY).

[originally from svn r3966]