Handle symbols as well as strings in the "source" lists of
netlist files.
Handle Protex gerber file extensions.
Check for project_name-whatever pattern for files that we
don't recognize (such as project_name-NPTH-drl_map.ps)
Mainly replacing std::string by wxString to manage filenames.
On Windows, a sdt::string cannot manage a filename, unless using
in many places TO_UTF8 and FROM_UTF8.
So the best way is to use a wxString for filenames and error messages.
It's a bit of a hack because they're statically initialized and
so we can't make use of the _() macro. We do still want it in the
code, however, because the string harvesting is based off of it.
Fixes: lp:1833000
* https://bugs.launchpad.net/kicad/+bug/1833000
