Potential fix for #41: avoid running tests twice

Rename ``test()`` to ``run()`` but use ``from import as`` to patch ``run()`` as
``blosc.test()``

```console
$ PYTHONPATH=. nosetests --with-doctest
................
----------------------------------------------------------------------
Ran 16 tests in 3.899s

OK
```

```pycon
In [1]: import blosc

In [2]: blosc.test()
test_basic_codec (blosc.test.TestCodec) ... ok
test_compress_exceptions (blosc.test.TestCodec) ... ok
test_compress_ptr_exceptions (blosc.test.TestCodec) ... ok
test_decompress_exceptions (blosc.test.TestCodec) ... ok
test_decompress_ptr_exceptions (blosc.test.TestCodec) ... ok
test_pack_array_exceptions (blosc.test.TestCodec) ... ok
test_set_nthreads_exceptions (blosc.test.TestCodec) ... ok
test_unpack_array_exceptions (blosc.test.TestCodec) ... ok
compress (blosc.toplevel)
Doctest: blosc.toplevel.compress ... ok
compress_ptr (blosc.toplevel)
Doctest: blosc.toplevel.compress_ptr ... ok
decompress (blosc.toplevel)
Doctest: blosc.toplevel.decompress ... ok
decompress_ptr (blosc.toplevel)
Doctest: blosc.toplevel.decompress_ptr ... ok
free_resources (blosc.toplevel)
Doctest: blosc.toplevel.free_resources ... ok
pack_array (blosc.toplevel)
Doctest: blosc.toplevel.pack_array ... ok
set_nthreads (blosc.toplevel)
Doctest: blosc.toplevel.set_nthreads ... ok
unpack_array (blosc.toplevel)
Doctest: blosc.toplevel.unpack_array ... ok

----------------------------------------------------------------------
Ran 16 tests in 3.404s

OK
```
Merge pull request #42 from esc/fix_test_runner

Potential fix for #41: avoid running tests twice