Remove unnecessary bends in inner segments
Remove unnecessary bends in inner segments

The previous definition of inner segment was not quite correct. It
treated any segment that was incident on a dummy node as an inner
sgement. Correct handling requires treating only edges that are incident
on two dummy nodes as inner segments.

Fixes #24.

rwl/dagre_charted,abduld/dagre,lmcorbo/dagre,cpettitt/dagre,cpettitt/dagre-d3,shelsonjava/dagre,leMaik/graphlib-dot,dagrejs/dagre-d3,git-ashish/dagre-d3,rwl/graphlib_dot,GerHobbelt/dagre,cpettitt/dagre,9n/dagre,shelsonjava/dagre,ENCODE-DCC/dagre-d3,cbfx/dagre-d3,cbfx/dagre-d3,git-ashish/dagre-d3,tylingsoft/dagre-layout,kdawes/dagre,rwl/dagre_charted,rwl/dagre,leMaik/graphlib-dot,cpettitt/graphlib-dot,9n/dagre-d3,dominiek/dagre-d3,9n/dagre,abduld/dagre,abduld/dagre,tylingsoft/dagre-layout,kdawes/dagre,cpettitt/dagre-d3,lmcorbo/dagre,cpettitt/dagre,shelsonjava/dagre,9n/dagre,dagrejs/dagre-d3,rwl/dagre_charted,git-ashish/dagre-d3,GerHobbelt/dagre,cpettitt/graphlib-dot,witcxc/dagre,ENCODE-DCC/dagre-d3,harsha-mudi/dagre-d3,dominiek/dagre-d3,cbfx/dagre-d3,GerHobbelt/dagre,cpettitt/dagre-d3,lmcorbo/dagre,dominiek/dagre-d3,9n/dagre-d3,harsha-mudi/dagre-d3,witcxc/dagre,kdawes/dagre,9n/dagre-d3