Fixed the cmake default which did not select the build type that it said.

The default is now really RelWithDebInfo.
As a byproduct, the backtrace is now leak-free (the leaky line number feature (in SLC5) is only present in Debug builds).
Relaxed the compilation for files with strict aliasing issues.
Gave a default value to a few variables which might e used uninitialized.
The unit tests hence pass again in SLC5.