0027282: [Regression to 6.9.1] smesh/bugs_00/A6: Cut produces an empty shape

0027282: [Regression to 6.9.1] smesh/bugs_00/A6: Cut produces an empty shape

1. The reason of the regression is not-closed intersection result. This problem has been solved (in this fix) by adding joint point to the both neighbors intersection lines (lines were extended to the this intersection point). It is made in IntPatch_WLineTool::ExtendTwoWlinesToEachOther(...) method.

2. Interface of IntPatch_PointLine and inherited classes has been changed. Methods ChangeVertex(...) and RemoveVertex(...) have been added.

Test cases for this issue have been created.

Small correction in the code.