minor fix - dx in integral should be abs(dx)
minor fix - dx in integral should be abs(dx)

--HG--
branch : pyspeckit

mikelum/pyspeckit,jpinedaf/pyspeckit,allisony/pyspeckit,allisony/pyspeckit,bsipocz/pyspeckit,jpinedaf/pyspeckit,vlas-sokolov/pyspeckit,low-sky/pyspeckit,low-sky/pyspeckit,keflavich/pyspeckit-obsolete,pyspeckit/pyspeckit,bsipocz/pyspeckit,e-koch/pyspeckit,pyspeckit/pyspeckit,mikelum/pyspeckit,dinossimpson/pyspeckit,dinossimpson/pyspeckit,keflavich/pyspeckit,vlas-sokolov/pyspeckit,keflavich/pyspeckit,e-koch/pyspeckit