Diagnostics can be required on both instance and session level,
so both cases need to be handled explicitly.
In addition, some reinterpret_casts were changed into static_casts.
Reinterpret_cast needs to be used with the instance, which is a
void** but static_cast is sufficient for the session, which is void*.
C++ header files have the .hh-suffix to distinguish them from C
header files, but also to allow a C++ header file (e.g. xyz.hh) for
an existing C header file (e.g. xyz.h).
- cpp.hh : Basic C++ stuff. Introduces the namespace "maxscale"
and its synonym "mxs".
- filter.[hh|cc]: Template class Filter and companion class FilterSession
to be used when implementing filters in C++.
- spinlock.h : Wrapper and lock guard class for SPINLOCK.
