Make textballon example follow convention

Currently, the qml examples autotest works on a set of conventions
defined in its source code to determine which tests to run.

examples/declarative/painteditem/textballoons/TextBalloonPlugin/plugin.h

@@ -41,7 +41,7 @@
 
 #include <QDeclarativeExtensionPlugin>
 
-#include "textballoon.h"
+#include "../textballoon.h"
 
 class TextBalloonPlugin : public QDeclarativeExtensionPlugin
 {

examples/declarative/painteditem/textballoons/textballoons.pro

@@ -5,9 +5,9 @@ QT += declarative
 TARGET = qmltextballoonplugin
 
 HEADERS += textballoonplugin/plugin.h \
-    textballoonplugin/textballoon.h
+    textballoon.h
 
-SOURCES += textballoonplugin/textballoon.cpp
+SOURCES += textballoon.cpp
 
 DESTDIR = textballoonplugin