Some cleanup in the C++ preprocessor.

Introduced pp-scanner.cpp, renamed `pp' to `Preprocessor' and removed useless #includes.

src/libs/cplusplus/pp-client.h

@@ -31,8 +31,8 @@
 **
 ***************************************************************************/
 
-#ifndef PP_CLIENT_H
-#define PP_CLIENT_H
+#ifndef CPLUSPLUS_PP_CLIENT_H
+#define CPLUSPLUS_PP_CLIENT_H
 
 #include <CPlusPlusForwardDeclarations.h>
 
@@ -79,4 +79,4 @@ public:
 
 } // namespace CPlusPlus
 
-#endif // PP_CLIENT_H
+#endif // CPLUSPLUS_PP_CLIENT_H