setup better paths, use Debian-specific systemd clean up logic instead of hacking around manually, improve README

debian/etc/taler.conf

@@ -0,0 +1,5 @@
+[PATHS]
+
+# Move runtime data "tmp" directory to /var/lib/taler-exchange/
+# to possibly provide additional protection from unwarranted access.
+TALER_RUNTIME_DIR = /var/lib/taler-exchange/tmp/

debian/taler-exchange.README.Debian

@@ -1,16 +1,22 @@
 taler-exchange
 --------------
 
-By default, the Taler exchange will start automatically when the system is booted.
-If you prefere to start it manually when you use it, change its configuration
-with:
-
-  # dpkg-reconfigure -plow taler-exchange
+Note that the configuration installed in /etc/taler.conf is incomplete and
+that Debian cannot launch an exchange with this minimal template. You must
+setup the currency, denominations and bank account access details before
+launching the Taler exchange can possibly succeed.
 
 In order to start, stop or restart manually the server, use:
 
-  # /etc/init.d/taler-exchange
+  # systemctl start taler-exchange
+  # systemctl stop taler-exchange
+  # systemctl restart taler-exchange
 
-with the parameter start, stop or restart.
+To permanently the exchange whenever the system boots, use:
+
+  # systemctl enable taler-exchange
+
+None of these are done by the Debian package because we cannot provide the
+required complete configuration details.
 
  -- Christian Grothoff <grothoff@gnu.org>  Mon 28 Dec 2020 11:37:14 AM CET

debian/taler-exchange.postinst

@@ -179,6 +179,11 @@ EOF
 		cp -f "${CONFIG_NEW}" "${CONFIG_FILE}"
 		echo " done."
 
+        mkdir -p /var/lib/taler-exchange/tmp
+        chown root:taler /var/lib/taler-exchange/tmp
+        chmod 770 /var/lib/taler-exchange/tmp
+        chmod +s /var/lib/taler-exchange/tmp
+
 		# Cleaning
 		rm -f "${CONFIG_NEW}"
 		echo "All done."

debian/taler-exchange.postrm

@@ -65,12 +65,6 @@ case "${1}" in
 		fi
 
 		rm -rf /var/log/taler/ /var/lib/taler /etc/default/taler
-        for X in httpd helper-rsa helper-eddsa wirewatch transfer
-        do
-            rm -f /etc/systemd/system/taler-exchange-${X}.service
-        done
-        systemctl daemon-reload
-
 		;;
 
 	remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)

debian/taler-exchange.postrm.debhelper

@@ -0,0 +1,6 @@
+# Automatically added by dh_installdebconf/13.3
+if [ "$1" = purge ] && [ -e /usr/share/debconf/confmodule ]; then
+	. /usr/share/debconf/confmodule
+	db_purge
+fi
+# End automatically added section