use macro for /usr/local/plan9

man/man4/9pserve.4

@@ -43,4 +43,4 @@ instead.
 .IR intro (4),
 .IR intro (9p)
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/9pserve.c
+.B \*9/src/cmd/9pserve.c

man/man4/acme.4

@@ -400,7 +400,7 @@ Text written to
 .B tag
 is always appended; the file offset is ignored.
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/acme
+.B \*9/src/cmd/acme
 .SH SEE ALSO
 .IR rio (1),
 .IR acme (1)

man/man4/plumber.4

@@ -101,7 +101,7 @@ no new messages will be delivered there).
 .B /usr/$user/lib/plumbing
 default rules file
 .TP
-.B /usr/local/plan9/plumb
+.B \*9/plumb
 directory to search for files in
 .B include
 statements
@@ -110,7 +110,7 @@ statements
 mount name for
 .IR plumber (4).
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/plumb
+.B \*9/src/cmd/plumb
 .SH "SEE ALSO"
 .IR plumb (1),
 .IR plumb (3),

man/man4/ramfs.4

@@ -44,7 +44,7 @@ This program is useful mainly as an example of how
 to write a user-level file server.
 It can also be used to provide high-performance temporary files.
 .SH SOURCE
-.B /usr/local/plan9/src/cmd/ramfs.c
+.B \*9/src/cmd/ramfs.c
 .SH "SEE ALSO"
 .IR 9p (3),
 .IR 9pserve (4)