Pcbnew: Plot files: for copper layers, create suffix from user copper layer names instead of default copper layer names, like in last stable Kicad version (bzr 4022), to build the plot files filenames.
Better test of illegal chars in plot filename, both in plot dialog and functions aclled by Python scripts.
Fix a Plotcontroller issue to make SetUseGerberExtensions() work as expected from Python scripts ( from Henner Zeller'patch with a fix to be sure it works properly from a Python script)
Note also using Protel Gerber Extensions is now a bad practice, because the official Gerber extension is .gbr since X2 Gerber version. But some users still use them)
jean-pierre charras
John Beard