Rename the DIAGNOSTICS sections in several man pages

to RETURN VALUES like they should be.

lib/libc/sys/getpeername.2

@@ -77,7 +77,7 @@ Before returning,
 .Fn getpeername
 unlocks
 .Va s .
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 A 0 is returned if the call succeeds, -1 if it fails.
 .Sh ERRORS
 The call succeeds unless:

lib/libc/sys/getsockname.2

@@ -75,7 +75,7 @@ Before returning,
 .Fn getsockname
 unlocks
 .Va fd .
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 A 0 is returned if the call succeeds, -1 if it fails.
 .Sh ERRORS
 The call succeeds unless:

lib/libc/sys/intro.2

@@ -46,7 +46,7 @@ their error returns, and other common definitions and concepts.
 .\".Sy System call restart
 .\".Pp
 .\"<more later...>
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 Nearly all of the system calls provide an error number referenced via
 the external identifier errno. This identifier is defined in 
 .Aq Pa sys/errno.h

lib/libc/sys/shutdown.2

@@ -57,7 +57,7 @@ is 1, further sends will be disallowed.
 If
 .Fa how
 is 2, further sends and receives will be disallowed.
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 A 0 is returned if the call succeeds, -1 if it fails.
 .Sh ERRORS
 The call succeeds unless:

lib/libc/sys/socketpair.2

@@ -58,7 +58,7 @@ are returned in
 and
 .Fa sv Ns [1] .
 The two sockets are indistinguishable.
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 A 0 is returned if the call succeeds, -1 if it fails.
 .Sh ERRORS
 The call succeeds unless:

lib/libc/sys/vfork.2

@@ -30,7 +30,7 @@
 .\" SUCH DAMAGE.
 .\"
 .\"     @(#)vfork.2	8.1 (Berkeley) 6/4/93
-.\"	$Id$
+.\"	$Id: vfork.2,v 1.5 1996/12/23 23:09:41 wosch Exp $
 .\"
 .Dd June 4, 1993
 .Dt VFORK 2
@@ -94,7 +94,7 @@ since buffered data would then be flushed twice.)
 .Xr fork 2 ,
 .Xr sigvec 2 ,
 .Xr wait 2
-.Sh DIAGNOSTICS
+.Sh RETURN VALUES
 Same as for
 .Xr fork 2 .
 .Sh BUGS