remove incorrect escaping of '+', correctly escape '-', and garbage collect .Tn

usr.bin/diff/diff.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: diff.1,v 1.47 2015/11/24 19:35:41 jmc Exp $
+.\" $OpenBSD: diff.1,v 1.48 2019/03/20 04:38:10 schwarze Exp $
 .\"
 .\" Copyright (c) 1980, 1990, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -29,7 +29,7 @@
 .\"
 .\"     @(#)diff.1	8.1 (Berkeley) 6/30/93
 .\"
-.Dd $Mdocdate: November 24 2015 $
+.Dd $Mdocdate: March 20 2019 $
 .Dt DIFF 1
 .Os
 .Sh NAME
@@ -107,11 +107,11 @@ by a line with fifteen
 The lines removed from
 .Ar file1
 are marked with
-.Sq \&-\ \& ;
+.Sq \-\ \& ;
 those added to
 .Ar file2
 are marked
-.Sq \+\ \& .
+.Sq +\ \& .
 Lines which are changed from one file to the other are marked in
 both files with
 .Sq !\ \& .
@@ -183,9 +183,7 @@ a single section.
 Comparison options:
 .Bl -tag -width Ds
 .It Fl a
-Treat all files as
-.Tn ASCII
-text.
+Treat all files as ASCII text.
 Normally
 .Nm
 will simply print
@@ -304,8 +302,7 @@ Binary files which differ,
 common subdirectories, and files which appear in only one directory
 are described as such.
 In directory mode only regular files and directories are compared.
-If a non-regular file such as a device special file or
-.Tn FIFO
+If a non-regular file such as a device special file or FIFO
 is encountered, a diagnostic message is printed.
 .Pp
 If only one of