Debugging helpers: Fix building

- Report errors correctly.
- Do not pass empty target argument to qmake
- Give 'make' a longer timeout and change timeout checking to
  trigger after last output line was obtained from process
- Make build log dialog non-modal and ensure it pops up on failure
  even if a different Qt version was selected in-between
- Disable Rebuild-button while build is running.

Reviewed-by: Kai Köhne <kai.koehne@nokia.com>
Reviewed-by: Lasse Holmstedt <lasse.holmstedt@nokia.com>

src/plugins/qt4projectmanager/qmlobservertool.cpp

@@ -99,13 +99,15 @@ QStringList QmlObserverTool::locationsByInstallData(const QString &qtInstallData
     return result;
 }
 
-QString QmlObserverTool::build(const QString &directory, const QString &makeCommand,
-                     const QString &qmakeCommand, const QString &mkspec,
-                     const Utils::Environment &env, const QString &targetMode)
+bool  QmlObserverTool::build(const QString &directory, const QString &makeCommand,
+                             const QString &qmakeCommand, const QString &mkspec,
+                             const Utils::Environment &env, const QString &targetMode,
+                             QString *output,  QString *errorMessage)
 {
     return buildHelper(QCoreApplication::translate("Qt4ProjectManager::QmlObserverTool", "QMLObserver"),
                        QLatin1String("qmlobserver.pro"),
-                       directory, makeCommand, qmakeCommand, mkspec, env, targetMode);
+                       directory, makeCommand, qmakeCommand, mkspec, env, targetMode,
+                       output, errorMessage);
 }
 
 static inline bool mkpath(const QString &targetDirectory, QString *errorMessage)