Otherwise libcppyy and libcppyy_backend are generated with the
.dylib suffix on OSX. This causes a crash when importing cppyy,
since it tries to load "libcppyy_backend.so" using ctypes.

They were ignored until now.

Without this, reading the same entry in 2 consecutive file (without reading any other entries
in between) fails thanks to the optimization avoiding to call GetEntry a 2nd time on the same
entry.

The IsZombie state/bit can not be reset from outside TObject.

Switch from active monitoring at each 'GetEntry' to using LoadTree's callback.

Cover all the error code from TChain/TTree::LoadTree

The earlier return was a pessimisation in all case but when calling Next after reaching the last entry,
and was technically wrong as it did not take in consideration which entry was being asked for (so if

anybody but TTreeReader::Next called SetEntryBase it could have return the wrong result

Switch from active monitoring at each 'GetEntry' to using LoadTree's callback.

https://github.com/apache/arrow/pull/2592

Using Long_t is obviously wrong.

Where T is a basic numeric type for arrow. The arrow types get mapped on
top of an RVec<STD_T> where STL_T is the equivalent C++ type.

Apparently this changed at some point. See also:

https://github.com/root-project/root/commit/cff35e0a6448d34146557455465267cbfb4638bf

Move declaration of ESockOptions and ESendRecvOptions enums from TSocket.h to TSystem.h, to get rid of this include dependencies in CMake:
include_directories(${CMAKE_SOURCE_DIR}/net/net/inc)

in order to allow to call ROOT::EnableImplicitMT() without including
that header.