(useful for boards having more than 2 layers)
Eeschema:fix compatibility with old schematic files, when they contain ERC markers.
Pcbnew: better test for allowed layers when creating/editing Dimensions and some other Graphic items
Drc: fix comments and messages for some drc tests.
Fix minor bugs in cleanup dialog options and plot solder mask function (thanks to Lorenzo to locate these bugs)
Pcbnew: better test for allowed layers when creating/editing Dimensions and some other Graphic items
Drc: fix comments and messages for some drc tests.
To do: fix issues in active layer selection when creating a track and layer pair selection dialog