Built Enable/Kiva may be binary-incompatible with older NumPy versions

[aaronayres35]

This is the sister issue to enthought/chaco#778

See the above issue for the full saga. In summary, enable will be built using the latest numpy, but an older version of numpy may be what exists in the environment after it is built. This can lead to unexpected/confusing segfaults and compatibility issues.

See comment: enthought/chaco#778 (comment) for a promising approach to a resolution.