Allow an open path to be saved/loaded where the start and end points share the exact same x/y coordinates.

A new flag spline flag 0x400 is used to explicitly store that this
point is the last point in an open path and must not be implicitly
connected to the first point in the spline because that is not how it
was when the file was saved.

The spline flag is at the end of the line after the 'c' curveto indicator
http://fontforge.org/sfdformat.html#Outline-Char-Data