Added exclusive locking for POSIX serial ports.
diff --git a/serial/serialutil.py b/serial/serialutil.py
index 636a10c..37eb321 100644
--- a/serial/serialutil.py
+++ b/serial/serialutil.py
@@ -185,6 +185,7 @@
                  write_timeout=None,
                  dsrdtr=False,
                  inter_byte_timeout=None,
+                 exclusive=None,
                  **kwargs):
         """\
         Initialize comm port object. If a "port" is given, then the port will be
@@ -211,6 +212,7 @@
         self._rts_state = True
         self._dtr_state = True
         self._break_state = False
+        self._exclusive = None
 
         # assign values using get/set methods using the properties feature
         self.port = port
@@ -224,6 +226,8 @@
         self.rtscts = rtscts
         self.dsrdtr = dsrdtr
         self.inter_byte_timeout = inter_byte_timeout
+        self.exclusive = exclusive
+        
         # watch for backward compatible kwargs
         if 'writeTimeout' in kwargs:
             self.write_timeout = kwargs.pop('writeTimeout')
@@ -305,6 +309,18 @@
             self._reconfigure_port()
 
     @property
+    def exclusive(self):
+        """Get the current exclusive access setting."""
+        return self._exclusive
+    
+    @exclusive.setter
+    def exclusive(self, exclusive):
+        """Change the exclusive access setting."""
+        self._exclusive = exclusive
+        if self.is_open:
+            self._reconfigure_port()
+
+    @property
     def parity(self):
         """Get the current parity setting."""
         return self._parity