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
Acceleration control. #185
Remove leftover M501
842, 847 slightly enlarge a clip polygon to counteract integer truncation

Geomery in referenced issues triggered Clipper problems, but also
pointed to a situation where integer truncation (as coordinates pass
into Clipper) might be shrinking a clip polygon in a way that leaves
degenerate or unwanted thin clip results. Growing the clip polygon by 2
is expected to overcome any issues caused by truncation of floats.
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
Bugfix: crash when reading/writing files to paths containing non-ASCII characters on Windows. #651 #865
offset miter limit to 3 - 801 828 836 851 875 - spikes and pimples

Was set to 10 to address 801. Setting to 3 has the same effect for 801,
and avoids spike artifacts that are likely causing "spike and pimple"
problems in the referenced issues.
extraneous fill against sloped walls with fill every N layers #834

Polygons used for N x depth fill surfaces need to be offset
by flow spacing before they are reused to clip lower fill surfaces.
Otherwise thin fill sections remain on clipped layers against sloping
walls, and the N x depth fill collides with them.
Ignore perimeter_acceleration and infill_acceleration if their values are 25 and 50 to handle legacy configs gracefully.
use infill flow spacing, not perimeter, for combine_infill() clip offsets