Manual rebase of the avoid_crossing_perimeters feature
Make the motionplanner work again after recent changes to approximation
Better implementation of the external motion planner
External motion was crossing still too much
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	README.markdown
	lib/Slic3r/ExPolygon.pm
	slic3r.pl
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	README.markdown
	lib/Slic3r/Config.pm
	lib/Slic3r/GCode.pm
	lib/Slic3r/Print.pm
	slic3r.pl
Merge branch 'master' into avoid-crossing-perimeters
Restore non-manifold warnings
Little cleanup
Bugfix: --avoid-crossing-perimeters was crashing when processing empty layers
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	lib/Slic3r/GCode.pm
Added Preferences dialog
Simple mode
Merge branch 'master' into avoid-crossing-perimeters

Conflicts:
	lib/Slic3r/GCode.pm
	lib/Slic3r/GUI/Plater.pm
	lib/Slic3r/Print.pm
	lib/Slic3r/SVG.pm
Raise max temperatures (in GUI) to 400°C
Replace 'Less' with 'Fewer' in plater. #944
Bugfix: the non-manifold warning was spitting out wrong coordinates
avoid DBus related crash on Ubuntu #954

An undocumented feature of Net::DBus->session() is that it returns
the same connection object it creates the first time it's called for
all subsequent calls. Somehow this exposes us to a bug where unref()
is called on that object too many times, causing a segfault.
Undefining the cached object after we've used it once avoids this.
harmless misplaced semicolon
Support .gco extension too. #957