Make 'mock' a run-time rather than setup-time dependency. This is necessary in order for 'tahoe debug trial' to work. refs #1296

src/allmydata/_auto_deps.py

@@ -30,6 +30,9 @@ install_requires=[
                   "pycrypto == 2.0.1, == 2.1, >= 2.3",
                   "pyasn1 >= 0.0.8a",
 
+                  # http://www.voidspace.org.uk/python/mock/
+                  "mock",
+
                   # Will be needed to test web apps, but not yet. See #1001.
                   #"windmill >= 1.3",
                   ]