Rewrite page(2) references to page(3).

Add description of new libmach.
diff --git a/man/man3/getwd.3 b/man/man3/getwd.3
index 021e5cd..24bdc83 100644
--- a/man/man3/getwd.3
+++ b/man/man3/getwd.3
@@ -24,10 +24,10 @@
 .B /sys/src/libc/9sys/getwd.c
 .SH "SEE ALSO"
 .IR pwd (1),
-.IR fd2path (2)
+.IR fd2path (3)
 .SH DIAGNOSTICS
 On error, zero is returned.
-.IR Errstr (2)
+.IR Errstr (3)
 may be consulted for more information.
 .SH BUGS
 Although the name returned by