Fixed an issue with creating transverse curves.

It was a non-trivial problem that when the bottom side was Moebius, and
there were flips (e.g. the RP2 Arnoux-Yoccoz), transverse curves were
not generated correctly, because the way the "sides" were defined
throughout the program.

Now two different notions of "side" exist: raw_side and adj_side, also,
points have raw_point and adj_point representions. "raw" is the old
notion, when if the bottom side is Moebius, everything on the top side
has side 0. The "adj" is the new notion when the picture is wrapped
along two sides of the interval [0,1], so points with raw_point less
than 0.5 have adj_side 0, the rest adj_side 1.

These changes affected many parts of the program, at most places leading
the more elegant code (e.g. separatrix, foliation_latex), but also
causing some little complications with the surface-orienting double
cover. All seems working now.