[Swan-dev] always generating the man page

[D. Hugh Redelmeier]

| From: Paul Wouters <paul at nohats.ca>

| But since we don't export a shared library, we don't have a devel
| package that would include the headers and developer man pages....

Right.  Simplest solution that kind of works:  build those manpages,
but don't install them.  Why build them?  Because they are hard to
read otherwise.  This wasn't true in Henry's day (because we wrote
directly in *roff).

Refinement: add a new makefile target (say: install-dev-manpages) that
would install those manpages.  The modest advantage of installing is
that "man -k" can then find them.