Suppress foolscap deprecation warnings, bug reported by Satra.

Now we import foolscap components according to their api.  I think
these four files contain all the naked 'from foolscap import'
statements we had, so all such warnings should be gone now.

IPython/kernel/enginefc.py

@@ -31,7 +31,13 b' from zope.interface import Interface, implements, Attribute'
 from twisted.internet.base import DelayedCall
 DelayedCall.debug = True
 
+try:
+    # This is preferred in foolscap v > 0.4.3
+    from foolscap.api import Referenceable, DeadReferenceError
+except ImportError:
+    # Fallback for older versions
 from foolscap import Referenceable, DeadReferenceError
+
 from foolscap.referenceable import RemoteReference
 
 from IPython.kernel.pbutil import packageFailure, unpackageFailure

IPython/kernel/fcutil.py

@@ -17,6 +17,11 b' __docformat__ = "restructuredtext en"'
 
 import os
 
+try:
+    # This is preferred in foolscap v > 0.4.3
+    from foolscap.api import Tub, UnauthenticatedTub
+except ImportError:
+    # Fallback for older versions
 from foolscap import Tub, UnauthenticatedTub
 
 def check_furl_file_security(furl_file, secure):

IPython/kernel/multienginefc.py

@@ -24,6 +24,11 b' from zope.interface import Interface, implements'
 from twisted.internet import defer
 from twisted.python import components, failure, log
 
+try:
+    # This is preferred in foolscap v > 0.4.3
+    from foolscap.api import Referenceable
+except ImportError:
+    # Fallback for older versions
 from foolscap import Referenceable
 
 from IPython.kernel import error 

IPython/kernel/taskfc.py

@@ -25,6 +25,11 b' from zope.interface import Interface, implements'
 from twisted.internet import defer
 from twisted.python import components, failure
 
+try:
+    # This is preferred in foolscap v > 0.4.3
+    from foolscap.api import Referenceable
+except ImportError:
+    # Fallback for older versions
 from foolscap import Referenceable
 
 from IPython.kernel.twistedutil import blockingCallFromThread