Ignore deprecation warnings about numpy.oldnumeric

Fixes trac issue [#10734](http://trac.mantidproject.org/mantid/ticket/10734)

Tester: This should be tested on a system with `numpy v1.8` & `scipy v0.13`. Build the code and run `python -c "import mantid"`, you should see no warnings.

To check that all deprecation warnings have not been squashed you can use this script
```python
from mantid.simpleapi import CreateSampleWorkspace

ws = CreateSampleWorkspace()
ws.getNumberBins()
```
It should produce a warning about `getNumberBins` being deprecated