use a perl test for fd-cloexec to avoid testing the tester with the tester; improve fd-cloexec description

lksh.1

@@ -1,6 +1,6 @@
-.\" $MirOS: src/bin/mksh/lksh.1,v 1.5 2013/05/22 18:18:06 tg Exp $
+.\" $MirOS: src/bin/mksh/lksh.1,v 1.6 2015/03/20 23:37:29 tg Exp $
 .\"-
-.\" Copyright (c) 2008, 2009, 2010, 2012, 2013
+.\" Copyright (c) 2008, 2009, 2010, 2012, 2013, 2015
 .\"	Thorsten “mirabilos” Glaser <tg@mirbsd.org>
 .\"
 .\" Provided that these terms and disclaimer and all copyright notices
@@ -72,7 +72,7 @@
 .\" with -mandoc, it might implement .Mx itself, but we want to
 .\" use our own definition. And .Dd must come *first*, always.
 .\"
-.Dd $Mdocdate: May 22 2013 $
+.Dd $Mdocdate: March 20 2015 $
 .\"
 .\" Check which macro package we use, and do other -mdoc setup.
 .\"
@@ -245,11 +245,17 @@ passes through the errorlevel from the
 .Xr getopt 1
 command.
 .It
-.Nm lksh ,
-unlike
+Unlike
 .At
 .Nm ksh ,
-does not keep file descriptors \*(Gt 2 private.
+.Nm mksh
+in
+.Fl o Ic posix
+or
+.Fl o Ic sh
+mode and
+.Nm lksh
+do not keep file descriptors \*(Gt 2 private from sub-processes.
 .El
 .Sh SEE ALSO
 .Xr mksh 1