h5py: Test for custom float promotion fails on some architectures

I refreshed the Debian packaging with version 2.7.0rc2. This version fails to test on selected architectures, some of which are considered major ones.

All failing architectures report the following error log:

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FAIL: test_custom_float_promotion (h5py.tests.old.test_h5t.TestTypeFloatID)
Custom floats are correctly promoted to standard floats on read.
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Traceback (most recent call last):
  File "h5py/tests/old/test_h5t.py", line 187, in test_custom_float_promotion
    self.assert_(values.dtype == np.float32)
AssertionError: False is not true

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