Fix dependency checking for configure.h (v2)

Fix dependency checking for configure.h (v2)

Alon Bar-Lev indicated commit f27bf509315a48b0070294c3993a718df0c2626c
was missing proper dependency checking.  This patch corrects this and
fixes an issue when creating configure.h via make distcheck.

This is an enhanced version of the one sent to the openvpn-devel mailing
list April 13, 2010 [1], after having received some feedback from Gert
Doering, cleaning up configure_log.awk further.

[1] <http://thread.gmane.org/gmane.network.openvpn.devel/3410/focus=3491>

Signed-off-by: David Sommerseth <dazo@users.sourceforge.net>
Acked-by: Gert Doering <gert@greenie.muc.de>