Add a systemd user service as a backend for the D-Bus session services

On systems with a systemd user session and a D-Bus user bus that
uses it for activation, this ensures that syncevo-dbus-server ends
up in its own cgroup, instead of being treated as part of dbus.service.

If org._01.pim.contacts and org.syncevolution are activated in quick
succession, it also prevents a race condition that would make one of
the activations fail, similar to
<https://bugs.freedesktop.org/show_bug.cgi?id=53220> in
telepathy-mission-control.

src/dbus/server/org.syncevolution.service.in

@@ -1,3 +1,4 @@
 [D-BUS Service]
 Name=org.syncevolution
 Exec=@libexecdir@/syncevo-dbus-server @SYNCEVO_DBUS_SERVER_ARGS@
+SystemdService=syncevo-dbus-server.service

src/dbus/server/pim/org._01.pim.contacts.service.in

@@ -1,3 +1,4 @@
 [D-BUS Service]
 Name=org._01.pim.contacts
 Exec=@libexecdir@/syncevo-dbus-server @SYNCEVO_DBUS_SERVER_ARGS@
+SystemdService=syncevo-dbus-server.service

src/dbus/server/server.am

@@ -117,6 +117,7 @@ src_dbus_server_libsyncevodbushelper_la_CXXFLAGS = $(SYNCEVOLUTION_CXXFLAGS) $(C
 # Deal with .service, .desktop and startup script files.
 CLEANFILES += \
   $(src_dbus_server_service_files) \
+  $(src_dbus_server_systemd_files) \
   $(src_dbus_server_desktop) \
   $(src_dbus_server_script)
 
@@ -137,10 +138,18 @@ src_dbus_server_service_files_in = src/dbus/server/org.syncevolution.service.in
 src_dbus_server_service_files = $(src_dbus_server_service_files_in:.service.in=.service)
 src_dbus_server_servicedir = $(DBUS_SERVICES_DIR)
 src_dbus_server_service_DATA = $(src_dbus_server_service_files)
+
+src_dbus_server_systemd_files_in = src/dbus/server/syncevo-dbus-server.service.in
+src_dbus_server_systemd_files = $(src_dbus_server_systemd_files_in:.service.in=.service)
+src_dbus_server_systemddir = $(prefix)/lib/systemd/user
+src_dbus_server_systemd_DATA = $(src_dbus_server_systemd_files)
+
+# this works for both dbus and systemd service files
 src/dbus/server/%.service: src/dbus/server/%.service.in
 	@sed -e "s|\@libexecdir\@|$(libexecdir)|" -e "s|\@SYNCEVO_DBUS_SERVER_ARGS\@|$(SYNCEVO_DBUS_SERVER_ARGS)|" $< >$@
 
 if COND_DBUS_PIM
+# this shares syncevo-dbus-server.service
 src_dbus_server_service_files_in += \
   src/dbus/server/pim/org._01.pim.contacts.service.in
 
@@ -175,6 +184,7 @@ endif # COND_DBUS_PIM
 
 dist_noinst_DATA += \
   $(src_dbus_server_service_files_in) \
+  $(src_dbus_server_systemd_files_in) \
   $(src_dbus_server_script_in) \
   $(src_dbus_server_desktop_in)
 

src/dbus/server/syncevo-dbus-server.service.in

@@ -0,0 +1,7 @@
+[Unit]
+Description=personal information management synchronization service
+
+[Service]
+Type=dbus
+BusName=org.syncevolution
+ExecStart=@libexecdir@/syncevo-dbus-server @SYNCEVO_DBUS_SERVER_ARGS@