Added assertion, to stop it blowing up more obscurely a little later.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

tools/python/xen/xend/xenstore/xstransact.py

@@ -11,6 +11,8 @@ from xen.xend.xenstore.xsutil import xshandle
 class xstransact:
 
     def __init__(self, path):
+        assert path is not None
+        
         self.in_transaction = False # Set this temporarily -- if this
                                     # constructor fails, then we need to
                                     # protect __del__.