Revert "qt4 - Make errors dialog Application Modal."

This reverts commit f4e4ec78.
Non-modal errors are non-model errors, and we only use the error dialog
for non-modal errors (otherwise we use a critical message box). We need
the Qt4 UI to remain usable inspite of a continuous flow of error.

modules/gui/qt4/dialogs/errors.cpp

@@ -42,8 +42,6 @@ ErrorsDialog::ErrorsDialog( QWidget *parent, intf_thread_t *_p_intf )
     setWindowTitle( qtr( "Errors" ) );
     resize( 500 , 300 );
 
-    setWindowModality( Qt::ApplicationModal );
-
     QGridLayout *layout = new QGridLayout( this );
 
     QDialogButtonBox *buttonBox = new QDialogButtonBox;