A patch to make pandas install and use numpy if it doesn't find it on the target host

Pandas will normally fail to install if numpy is not installed on the target host. This should normally be resolved by specifying numpy as a dependency but Pandas will still require that numpy is installed first due to its need of the numpy include files.

This patch resolves this problem by changing the way the numpy include path is retrieved so that it is not necessary that numpy is first installed before pandas - they can both be installed together; numpy coming first of course.