Bug in GeomFill_Coons algorithm

Algorithm of building Coons surface has a bug: two surfaces built for C1 curves
have no C1 continuity along a common boundary.
Since there is no Draw command, which uses the Coons algorithm, to reproduce bug it is necessary to do the following:
1. Integrate attached file GeometryTest_SurfaceCommand.cxx with new Draw command
fillcurves res C1 C2 C3 C4 [Style]
2.Perform attached script srcipt.tcl:
restore c1
restore c2
restore c31
restore c32
restore c41
restore c42
restore cv
fillcurves s11 c1 c41 cv c31
fillcurves s12 cv c42 c2 c32
svalue s11 .5 .5 x1 y1 z1 dux1 duy1 duz1 dvx1 dvy1 dvz1
svalue s12 .5 .5 x2 y2 z2 dux2 duy2 duz2 dvx2 dvy2 dvz2
dval dvx1-dvx2
dval dvy1-dvy2
dval dvz1-dvz2

Result is:
-0.41063169232111768
0.74598350784300127
0.24020534108274028
But these values must be closed to zero
Correct result (after fixing bug) is:
4.[revision removed]-015
-4.[revision removed]-015
-2.[revision removed]-015