fix include style relating to cplusplus libraries

... and adjust INCLUDEPATH accordingly.

while i'm at messing with include statements, also re-order the include
blocks according to policy and sort them within bigger blocks.

Change-Id: I7762abfd7c4ecf59432b99db2f424e4fa25733a5
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/libs/cplusplus/pp-engine.h

@@ -52,8 +52,9 @@
 #include "PPToken.h"
 #include "PreprocessorClient.h"
 
-#include <Lexer.h>
-#include <Token.h>
+#include <cplusplus/Lexer.h>
+#include <cplusplus/Token.h>
+
 #include <QVector>
 #include <QBitArray>
 #include <QByteArray>