Fixed tracks of 0 width causing division by 0 error.
Changed BOARD_DESIGN_SETTINGS::m_VisibleElements from int to long, to assure at least 32 bits length (without depending on the platfrom int size).
Changed ROUTER_PREVIEW_ITEM layer.
Minor changes.
Moved netnames (GAL specific layers) to a separate enum, to avoid saving/reading their settings from files.
Added a check for the number of PCB_VISIBLE elements.
Worksheet & general purpose overlay layers are visible by default.
Reverted changes introduced by the revision 4655.
Moved PCB_VISIBLE size check to .cpp.
Pcbnew: fix OpenGL PNS router track not shown bug. (fixes lp:1275319)