iterate(): new function
iterate(): new function

Added unit tests for iterate.

VisTrails/VisTrails,hjanime/VisTrails,hjanime/VisTrails,Nikea/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,minesense/VisTrails,minesense/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,minesense/VisTrails,Nikea/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,celiafish/VisTrails,celiafish/VisTrails,Nikea/VisTrails