adjusted return behavior, corrected when there is a selection

previously, a return key only inserted a new line when at the end of a
non-blank line (use control+return key to always insert a new line);
adjusted behavior to also insert a new line on a blank line

when there was a selection, a return key ignored the selection an
advanced to the next line; this was corrected to replace the selected
text with a new line

when there was a selection across two lines with characters selected on
the second line, a control+return key correctly replaced the selection
with a new line, however, the edit box was not redrawn properly (the
selection remained on the screen, though text was not actually selected
and the text was removed from the document); this was corrected by
creating a new key press event with a no modified return key

editbox.cpp

@@ -82,16 +82,21 @@ void EditBox::keyPressEvent(QKeyEvent *event)
 	case Qt::Key_Return:
 	case Qt::Key_Enter:
 		// intercept Control+Return and change it to a Return event
-		if (event->modifiers() & Qt::ControlModifier
-			|| cursor.atBlockEnd() && !cursor.atBlockStart())
+		if (event->modifiers() & Qt::ControlModifier || cursor.atBlockEnd())
 		{
-			cursor.insertText("\n");
+			event = new QKeyEvent(QEvent::KeyPress, Qt::Key_Return,
+				Qt::NoModifier);
+			QPlainTextEdit::keyPressEvent(event);
+			delete event;
 			return;
 		}
 		else  // intercept Return when cursor is not at the end of a line
 		{
-			moveCursor(QTextCursor::NextBlock);
-			return;
+			if (!cursor.hasSelection())
+			{
+				moveCursor(QTextCursor::NextBlock);
+				return;
+			}
 		}
 		break;