Redo and enhance the support for building shared libraries. Currently

there's support for building under Linux and True64 (using examples
from the programming manuals), including versioning that is currently
the same as OpenSSL versions but should really be a different series.

With this change, it's up to the users to decide if they want shared
libraries as well as the static ones.  This decision now has to be
done at configuration time (well, not really, those who know what they
do can still do it the same way as before).

The OpenSSL programs (openssl and the test programs) are currently
always linked statically, but this may change in the future in a
configurable manner.  The necessary makefile variables to enable this
are in place.

Also note that I have done absolutely nothing about the Windows target
to get something similar.  On the other hand, DLLs are already the
default there, but without versioning, and I've no idea what the
possibilities for such a thing are there...