version dependency/tests on numexpr -- truediv etc are NA in numexpr 1.4.2
while building for Ubuntu 12.04, bulk of tests fail due e.g.
`ValueError: Unknown keyword argument 'truediv'` from numexpr and `AssertionError: Did not use numexpr as expected` in test_expressions

Full log http://neuro.debian.net/_files/_buildlogs/pandas/0.13.0/pandas_0.13.0-2~nd12.04+1_i386.build
