core, bridge, jp, quick_frontend: SàT stop more gracefully if bridge can't be initialised:

- new BridgeInitError and BridgeExceptionNoService are in core.exceptions
    - D-Bus NotSupported is catched in bridge, and launch a BridgeInitError
    - BridgeInitError stop SàT core, jp, and quick_frontends with an explanation message.
fix bug 27

frontends/src/quick_frontend/quick_app.py

@@ -17,9 +17,11 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import sys
 from logging import debug, info, warning, error
 from sat.tools.jid  import JID
-from sat_frontends.bridge.DBus import DBusBridgeFrontend,BridgeExceptionNoService
+from sat_frontends.bridge.DBus import DBusBridgeFrontend
+from sat.core.exceptions import BridgeExceptionNoService, BridgeInitError
 from sat_frontends.quick_frontend.quick_utils import escapePrivate, unescapePrivate
 from optparse import OptionParser
 
@@ -41,7 +43,9 @@ class QuickApp(object):
             self.bridge=DBusBridgeFrontend()
         except BridgeExceptionNoService:
             print(_(u"Can't connect to SàT backend, are you sure it's launched ?"))
-            import sys
+            sys.exit(1)
+        except BridgeInitError:
+            print(_(u"Can't init bridge"))
             sys.exit(1)
         self.bridge.register("connected", self.connected)
         self.bridge.register("disconnected", self.disconnected)