When producing man-pages, ensure NAME section is one line only

There are *roff parsers that are strict about the NAME section being
one line only.  The man(7) on Debian GNU/Linux suggests that this is
appropriate, so we compensate our multi-line NAME sections by fixing
the *roff output.

Noted by Eric S. Raymond

Related to #6264

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/6268)

(cherry picked from commit 8d483b2d)