Make pkidir, rundir, logdir modifiable from "configure" command line.

Make "make" behave properly when these are changed by re-running
"configure", by putting their definitions into a generated file that
depends on Makefile.

secchan/secchan.8.in

@@ -401,7 +401,7 @@ require the controller to send the CA certificate, but
 Causes a file (by default, \fBsecchan.pid\fR) to be created indicating
 the PID of the running process.  If \fIpidfile\fR is not specified, or
 if it does not begin with \fB/\fR, then it is created in
-\fB@rundir@\fR.
+\fB@RUNDIR@\fR.
 
 .TP
 \fB-f\fR, \fB--force\fR