* Fixed a bug in PCB_EDIT_FRAME::loadFootprints when no footprint libraries
  are found when attempting to load footprints.
* Add a warning to PCB_EDIT_FRAME::loadFootprints to inform the user when
  a footprint library file cannot be found in any of the standard library
  search paths.
* Changed FOOTPRINT_INFO::m_padCount to unsigned to prevent signed/unsigned
  comparison compiler warnings.
* Put NestedSpace() function in netlist_reader.cpp inside conditional debug
  build statement to prevent warning in release builds.