Add ability to source common configuration hook file(s).

--- ./vpnc-script	2019-10-16 22:56:48.581008713 +0000
+++ ./vpnc-script	2019-10-16 22:59:15.859322960 +0000
@@ -77,6 +77,9 @@ PATH=/sbin:/usr/sbin:$PATH
 
 OS="`uname -s`"
 
+# You can create sourcable scriptlets under "${HOOKS_DIR}/${HOOK}.d/"
+# where $HOOK is either one of the $reason's above, or "common-config"
+# which is sourced before other hooks when processing a valid reason.
 HOOKS_DIR=/etc/vpnc
 DEFAULT_ROUTE_FILE=/var/run/vpnc/defaultroute
 RESOLV_CONF_BACKUP=/var/run/vpnc/resolv.conf-backup
@@ -1022,20 +1025,24 @@ fi
 
 case "$reason" in
 	pre-init)
+		run_hooks common-config
 		run_hooks pre-init
 		do_pre_init
 		;;
 	connect)
+		run_hooks common-config
 		run_hooks connect
 		do_connect
 		run_hooks post-connect
 		;;
 	disconnect)
+		run_hooks common-config
 		run_hooks disconnect
 		do_disconnect
 		run_hooks post-disconnect
 		;;
 	attempt-reconnect)
+		run_hooks common-config
 		# Invoked before each attempt to re-establish the session.
 		# If the underlying physical connection changed, we might
 		# be left with a route to the VPN server through the VPN
@@ -1043,6 +1050,7 @@ case "$reason" in
 		run_hooks attempt-reconnect
 		;;
 	reconnect)
+		run_hooks common-config
 		# After successfully re-establishing the session.
 		run_hooks reconnect
 		;;