use macro for /usr/local/plan9
diff --git a/man/man3/needstack.3 b/man/man3/needstack.3
index 31588f6..cf13809 100644
--- a/man/man3/needstack.3
+++ b/man/man3/needstack.3
@@ -50,7 +50,7 @@
The X Window library implementation of
.I XLookupString
allocates some very large buffers on the stack, so
-.B /usr/local/plan9/src/libdraw/x11-itrans.c
+.B \*9/src/libdraw/x11-itrans.c
calls
.B needstack(20*1024)
before making calls to
@@ -62,8 +62,8 @@
does not allocate a large enough stack, the problem is diagnosed
immediately rather than left to corrupt memory.
.SH SOURCE
-.B /usr/local/plan9/src/lib9/needstack.c
+.B \*9/src/lib9/needstack.c
.br
-.B /usr/local/plan9/src/libthread
+.B \*9/src/libthread
.SH SEE ALSO
.IR thread (3)
