fixed hash issue with same base features

[gsheni]

if there is a feature which is the square of another feature, that would not be currently possible with our current feature primitive.

Feature(es["log"]["value"]) * Feature(es["log"]["value"])

So this fixes this by having the left and right point to the same element in base_features

[CLAassistant]

All committers have signed the CLA.

[kmax12]

can you add a test?

[kmax12]

looks good to me