Use .MR instead of .BR for manual page references

doc/trader.6

@@ -36,6 +36,13 @@
 .char \[hellip] ...\"		Three full stops
 .\}
 .\"
+.\" Define .MR page-topic page-section [trailing-text]
+.if !d MR \{\
+.de MR
+.IR \\$1 (\\$2)\\$3
+..
+.\}
+.\"
 .\" Define .URL, .MTO and .FTP, then try to load the www.tmac version
 .de URL
 \\$2 \(la\\$1\(ra\\$3
@@ -127,7 +134,7 @@ game 4, if it was previously saved:
 .RE
 If you are running under the X Window System, you might like to start the
 game in a dedicated
-.BR xterm (1)
+.MR xterm 1
 window (typed all on one line):
 .RS
 .sp
@@ -176,7 +183,7 @@ Star Traders uses the Curses library for displaying text on the screen.
 As such, it will access these two environment variables if the underlying
 Curses library does so (see, for example, the \fBENVIRONMENT\fP section
 in the
-.BR ncurses (3)
+.MR ncurses 3
 manual page for in-depth details).  It requires a text console or window
 of at least 80\(mu24 in size.
 .TP
@@ -187,9 +194,9 @@ appropriate settings.  In particular, messages will be displayed using
 into that language).  In addition, numeric quantities will be displayed
 using \fBLC_NUMERIC\fP and monetary quantities will use
 \fBLC_MONETARY\fP.  See the
-.BR locale (7)
+.MR locale 7
 or
-.BR setlocale (3)
+.MR setlocale 3
 manual pages for more details on locale settings.
 .TP
 .B TEXTDOMAINDIR