Changed ground_motion_fields to expand the result only if a non-trivial filter is passed
Merge branch 'master' into gmf-no-expand
Updated a docstring
Merge branch 'master' of https://github.com/gem/oq-hazardlib into removing-ruptures-3
Merge pull request #168 from gem/removing-ruptures-3

Expand the result of calc.gmf.ground_motion_fields only if a nontrivial filtering function is passed