ENH: Add input validation to attach_pipeline.
ENH: Add input validation to attach_pipeline.

humdings/zipline,Scapogo/zipline,bartosh/zipline,alphaBenj/zipline,florentchandelier/zipline,enigmampc/catalyst,quantopian/zipline,Scapogo/zipline,quantopian/zipline,humdings/zipline,magne-max/zipline-ja,enigmampc/catalyst,magne-max/zipline-ja,alphaBenj/zipline,bartosh/zipline,florentchandelier/zipline