Set up configuration file for Debian properly

dist/debian/arsse.links

@@ -0,0 +1 @@
+etc/arsse/config.php usr/share/arsse/config.php

dist/debian/arsse.postinst

@@ -4,6 +4,9 @@ set -e
 
 . /usr/share/debconf/confmodule
 
+if [ "$1" = "configure" ]; then
+    # Set permissions on configuration file
+    dpkg-statoverride --list "/etc/arsse/config.php" >/dev/null || dpkg-statoverride --update --add root www-data 640 "/etc/arsse/config.php"
     # Set up dbconfig-common
     if test -f /usr/share/dbconfig-common/dpkg/postinst; then
         . /usr/share/dbconfig-common/dpkg/postinst
@@ -16,6 +19,7 @@ if test -f /usr/share/dbconfig-common/dpkg/postinst; then
         dbc_dbfile_perms="0660"
         dbc_go arsse "$@"
     fi
+fi
 
 # dh_installdeb will replace this with shell code automatically
 # generated by other debhelper scripts.