ENH:  Missed spec for generic computation type.

A recent patch made the point set metrics compatible
with double or float computation types.  However, I
missed a change in the ExpectationBasedPointSetMetric
class.  This patch fixes this omission.

Change-Id: I526b50f65ccc5a5805d64b2270f9226abd35b339
Merge topic 'PSEGenericComputationType'

446eabe0 ENH:  Missed spec for generic computation type.