Circumventing a node by adjacent facets

[rosoba]

The evaluation of angle-based criteria requires the detection of cycles around a node. Currently the line-based detection is used. The existence of a facet between the lines is not checked. Thus, a cut-off facet would be regarded as a normal facet.
This extension should be done together with the implicit derivation (addition) of lines based on the F_N mapping so that the L array could only contain just lines that are not attached to any facet.