check if avahi is available and we're not on windows,

otherwise checkbutton is not sensitive

data/glade/accounts_window.glade

@@ -95,7 +95,8 @@
       <child>
 	<widget class="GtkCheckButton" id="enable_zeroconf_checkbutton">
 	  <property name="visible">True</property>
-	  <property name="tooltip" translatable="yes">If checked, all local contacts that use a Bonjour compatible chat client (like iChat, Trillian or Gaim) will be shown in roster. You don't need a jabber server for it.</property>
+	  <property name="tooltip" translatable="yes">If checked, all local contacts that use a Bonjour compatible chat client (like iChat, Trillian or Gaim) will be shown in roster. You don't need to be connected to a jabber server for it to work.
+This is only available if python-avahi is installed and avahi-daemon is running.</property>
 	  <property name="can_focus">True</property>
 	  <property name="label" translatable="yes">_Enable link-local messaging</property>
 	  <property name="use_underline">True</property>

src/common/zeroconf/connection_zeroconf.py

@@ -256,6 +256,7 @@ class ConnectionZeroconf(ConnectionHandlersZeroconf):
 			self.zeroconf.disconnect()
 
 	def reconnect(self, new_port):
+		if self.connected:
 			txt = {}
 			txt['1st'] = gajim.config.get_per('accounts', gajim.ZEROCONF_ACC_NAME, 'zeroconf_first_name')
 			txt['last'] = gajim.config.get_per('accounts', gajim.ZEROCONF_ACC_NAME, 'zeroconf_last_name')

src/config.py

@@ -1790,10 +1790,20 @@ class AccountsWindow:
 		st = gajim.config.get('mergeaccounts')
 		self.xml.get_widget('merge_checkbutton').set_active(st)
 
+		import os
+
+		avahi_error = False
+		try:
+			import avahi
+		except ImportError:
+			avahi_error = True
+
 		# enable zeroconf
 		st = gajim.config.get('enable_zeroconf')
 		w = self.xml.get_widget('enable_zeroconf_checkbutton')
 		w.set_active(st)
+		if os.name == 'nt' or avahi_error:
+			w.set_sensitive(False)
 		w.connect('toggled', self.on_enable_zeroconf_checkbutton_toggled)
 
 	def on_accounts_window_key_press_event(self, widget, event):