GMR-187: fixes and improvements for ROOT 6.08 and gcc 6.1
apply Gaudi Merge Request 187: gaudi/Gaudi!187 (merged)
fixes and improvements for ROOT 6.08 and gcc 6.1
- added option to use or not GCC old C++11 ABI (off by default)
- added some missing #include for the usual headers clean up in gcc
- fixed a few places where old GCC behaviour was assumed
- fixed default C++ standard version for clang >= 3.7
- fixed GAUDI-1242