Fix rounding issue on generated GCODE

We store the X, Y, Z coordinates in microns, let's try to
keep as much precision and do not round to 2 digits after
the decimal point but 3 in generated GCODEs when converting
into mm.
Merge pull request #124 from foosel/fix/tooMuchRounding

Fix rounding issue on generated GCODE
Try to put the Z seam in internal corners instead of anywhere on the external face.
Some better parameters for the corner finding routine.
Cross hatch the first layer of line grids so you get better bed adheasion. Also expand these lines a bit more so they attach to a brim better, if there is a brim.
Fix build on linux.
Merge branch 'master' of https://github.com/Ultimaker/CuraEngine