Correct version of the SPD thermal screen for what concerns the so-called

Correct version of the SPD thermal screen for what concerns the so-called
"Omega shape".
Revised algorithm for computing the internal points, which should be
correct now.

-- a new version of AliITSv11GeometrySupport.h : prototypes of two new private
methods, modified prototype of another private method
-- a new version of AliITSv11GeometrySupport.cxx : implementation of the two
new methods (to compute the internal points of the shapes, i.e. the points of
the edges not in contact with the external shape), modified driving method to
compute those points.

Mario Sitta