tmac: rename IM (italic manual) to MR (manual reference)

Suggested by G. Brandon Robinson.

man/man4/9pserve.4

@@ -50,7 +50,7 @@ and clunks any outstanding fids belonging to the client.
 .PP
 .I 9pserve
 is typically not invoked directly; use
-.IM post9pservice (3)
+.MR post9pservice (3)
 instead.
 .PP
 The options are:
@@ -73,7 +73,7 @@ rewrite all attach messages to use
 and
 .IR afid ;
 used to implement
-.IM srv (4) 's
+.MR srv (4) 's
 .B -a
 option
 .TP
@@ -90,8 +90,8 @@ instead assume 9P2000 and a maximum message size of
 .IR msize
 .PD
 .SH "SEE ALSO
-.IM intro (4) ,
+.MR intro (4) ,
 .IR intro (9p),
-.IM 9pfuse (4)
+.MR 9pfuse (4)
 .SH SOURCE
 .B \*9/src/cmd/9pserve.c