Merged in masterschlumpf/beremiz/wx3-fix (pull request #37)

Fix an exception with wx-3.0-gtk3 in PLCOpenEditor when generating ST files

Approved-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>

                  <xsd:element name="Linux">
                    <xsd:complexType>
                      %(toolchain_gcc)s
                    </xsd:complexType>
                  </xsd:element>