Qt4ProjectConfigWidget: Update build directory line edit on build

That line edit shows a red text if the directory does not exist,
building triggers a recheck and removes the red if the directory exists.

Change-Id: I50e87816a3e1b4ee9ef6ccb91e66eec8f7783242
Reviewed-by: Robert Loehning <robert.loehning@digia.com>

src/libs/utils/pathchooser.cpp

@@ -426,6 +426,11 @@ QString PathChooser::errorMessage() const
     return d->m_lineEdit->errorMessage();
 }
 
+void PathChooser::triggerChanged()
+{
+    d->m_lineEdit->triggerChanged();
+}
+
 bool PathChooser::validatePath(const QString &path, QString *errorMessage)
 {
     QString expandedPath = d->expandedPath(path);

src/libs/utils/pathchooser.h

@@ -131,6 +131,7 @@ public:
     bool isReadOnly() const;
     void setReadOnly(bool b);
 
+    void triggerChanged();
 private:
     // Returns overridden title or the one from <title>
     QString makeDialogTitle(const QString &title);

src/plugins/qt4projectmanager/qt4projectconfigwidget.cpp

@@ -188,7 +188,7 @@ void Qt4ProjectConfigWidget::shadowBuildEdited()
 
 void Qt4ProjectConfigWidget::updateProblemLabel()
 {
-
+    m_ui->shadowBuildDirEdit->triggerChanged();
     ProjectExplorer::Kit *k = m_buildConfiguration->target()->kit();
     const QString proFileName = m_buildConfiguration->target()->project()->document()->fileName();