Regular checks, with a tunable frequency, of process memory were introduce as a first
  debug layer. However, they require calls to System::GetProcInfo which are particurarly
  heavy. Since by default this information is not used, it makes more sense to have it off.

Correct the insertion of the rootmapfile entry in the already seen forward decls. (ROOT-6063 and 6141).

- add only for clang compiler flag -Wno-unused-funciton to suppress the warning

(Thanks Bertrand to have seen it :-) )

To provide an example for the fix/change for ROOT-748 just committed.

To get the same behaviour as in Tree::Process.
The TSelector::fStatus of all non-aborted workers are added.

The 'simple' (TRadialGradient::kSimple) implemented with OpenGL.

Collect the already returned information to return 0 in case of success, -1 in the
case at leat one node did not manage to set the wanted version