tmac: introduce real manual reference macro instead of overloading IR

The overloading of IR emits magic \X'...' sequences that turn into HTML manual links.
But not all such IR invocations should be manual links;
those had to be written to avoid the IR macro before.
Worse, the \X'...' ending the IR causes troff to emit only a single space after a period.

Defining a new IM macro for manual references fixes both problems.

Fixes #441.

man/man3/pushtls.3

@@ -46,7 +46,7 @@ TLS is nearly the same as SSL 3.0, and the software should interoperate
 with implementations of either standard.
 .PP
 To use just the record layer, as described in Plan 9's
-\fItls\fR(3),
+.IR tls (3),
 call
 .I pushtls
 to open the record layer device, connect to the communications channel
@@ -108,7 +108,7 @@ used by a client to resume a previously negotiated security association.
 On output, the connection directory is set, as with
 .B listen
 (see
-.IR dial (3)).
+.IM dial (3) ).
 The input
 .I cert
 is freed and a freshly allocated copy of the remote's certificate
@@ -149,7 +149,7 @@ The private key corresponding to
 .I cert.pem
 should have been previously loaded into factotum.
 (See
-.IR rsa (3)
+.IM rsa (3)
 .\" XXX should be rsa(8)
 for more about key generation.)
 By setting
@@ -164,10 +164,10 @@ known to the client.
 is not required for the ongoing conversation and may
 be freed by the application whenever convenient.
 .SH FILES
-.TP 
+.TP
 .B /sys/lib/tls
 thumbprints of trusted services
-.TP 
+.TP
 .B /sys/lib/ssl
 PEM certificate files
 .SH SOURCE
@@ -175,12 +175,12 @@ PEM certificate files
 .\" .br
 .B \*9/src/libsec/port
 .SH "SEE ALSO"
-.IR dial (3),
-.IR thumbprint (7);
+.IM dial (3) ,
+.IM thumbprint (7) ;
 Plan 9's
-\fIfactotum\fR(4)
+.IR factotum (4)
 and
-\fItls\fR(3)
+.IR tls (3)
 .SH DIAGNOSTICS
 return \-1 on failure.
 .SH BUGS