setfsuid.2: Rewrite for improved clarity and to hint history more explicitly

The current text reads somewhat clumsily. Rewrite it to introduce
the eUID and fsUID in parallel, and more clearly hint at the the
historical rationale for the fsUID, which is detailed lower in
the page.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
1 file changed