Use the theme background color for panel line edits

Previously, the image used as background forced it to be white, which
made the text impossible to read when the palette foreground color
happened to be white as well.

Task-number: 258167
(cherry picked from commit 57bebee640)

src/plugins/coreplugin/manhattanstyle.cpp

@@ -474,6 +474,12 @@ void ManhattanStyle::drawPrimitive(PrimitiveElement element, const QStyleOption
     case PE_PanelLineEdit:
         {
             painter->save();
+
+            // Fill the line edit background
+            QRect filledRect = option->rect.adjusted(1, 1, -1, -1);
+            painter->setBrushOrigin(filledRect.topLeft());
+            painter->fillRect(filledRect, option->palette.base());
+
             if (option->state & State_Enabled)
                 drawCornerImage(d->lineeditImage, painter, option->rect, 2, 2, 2, 2);
             else

src/plugins/qt4projectmanager/qt4project.cpp

@@ -923,11 +923,6 @@ QList<BuildConfigWidget*> Qt4Project::subConfigWidgets()
     return subWidgets;
 }
 
-/// **************************
-/// Qt4ProjectBuildConfigWidget
-/// **************************
-
-
 void Qt4Project::collectApplicationProFiles(QList<Qt4ProFileNode *> &list, Qt4ProFileNode *node)
 {
     if (node->projectType() == Internal::ApplicationTemplate