Fix temporary file bug when saving modified footprints. (fixes lp:1384550)

* Use wxRenameFile which falls back to a file copy and file remove when
  wxRename fails.

pcbnew/kicad_plugin.cpp

@@ -246,7 +246,11 @@ void FP_CACHE::Save()
 
         wxRemove( fn.GetFullPath() );     // it is not an error if this does not exist
 
-        if( wxRename( tempFileName, fn.GetFullPath() ) )
+        // Even on linux you can see an _intermittent_ error when calling wxRename(),
+        // and it is fully inexplicable.  See if this dodges the error.
+        wxMilliSleep( 250L );
+
+        if( !wxRenameFile( tempFileName, fn.GetFullPath() ) )
         {
             wxString msg = wxString::Format(
                     _( "Cannot rename temporary file '%s' to footprint library file '%s'" ),

pcbnew/legacy_plugin.cpp

@@ -4487,7 +4487,7 @@ void LP_CACHE::Save()
     // and it is fully inexplicable.  See if this dodges the error.
     wxMilliSleep( 250L );
 
-    if( wxRename( tempFileName, m_lib_path ) )
+    if( !wxRenameFile( tempFileName, m_lib_path ) )
     {
         THROW_IO_ERROR( wxString::Format(
             _( "Unable to rename tempfile '%s' to library file '%s'" ),