Enable technical layers when starting Pcbnew with no board.

    m_gerberUnitInch = false;    // Currently fixed, but could be an option

    // number of digits after the point (number of digits of the mantissa

    // Be carefull: the coordinates are stored in an integer

    // so 6 digits (inches) or 5 digits (mm) is the best value

    // to avoid truncations and overflow

    m_gerberUnitFmt = m_gerberUnitInch ? 6 : 5;

    // Be carefull: the Gerber coordinates are stored in an integer

    // so 6 digits (inches) or 5 digits (mm) is a good value

    // To avoid overflow, 7 digits (inches) or 6 digits is a max.

    // with lower values than 6 digits (inches) or 5 digits (mm),

    // Creating self-intersecting polygons from non-intersecting polygons

    // happen easily.

    m_gerberUnitFmt = m_gerberUnitInch ? 7 : 6;

    m_IUsPerDecimil = aIusPerDecimil;

    iuPerDeviceUnit = pow( 10.0, m_gerberUnitFmt ) / ( aIusPerDecimil * 10000.0 );

    for( LAYER_NUM ii = LAYER_N_2; ii < aNewLayerCount - 1; ++ii )

        m_enabledLayers |= GetLayerSet( ii );

#else

    m_enabledLayers = LSET::AllCuMask( aNewLayerCount );

    // Update only enabled copper layers mask

    m_enabledLayers &= ~LSET::AllCuMask();

    m_enabledLayers |= LSET::AllCuMask( aNewLayerCount );

#endif

}