Document and improve system options definition in the environment.

Document that system options can be defined in the environment.

Replace another character (dash) invalid in environment variable names but
present in some standard system option names with underscore.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@64651 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/sysopt.cpp

@@ -83,6 +83,7 @@ wxString wxSystemOptions::GetOption(const wxString& name)
         // and then for "wx_name" which can be set to change the option globally
         wxString var(name);
         var.Replace(wxT("."), wxT("_"));  // '.'s not allowed in env var names
+        var.Replace(wxT("-"), wxT("_"));  // and neither are '-'s
 
         wxString appname;
         if ( wxTheApp )