Merged requested to merge fwinkl/athena:xaodroot2 into master
Mostly "cosmetic" thread-checker fixes as most of this code actually never runs multi-threaded:
Initand various const fixes and warning suppressions. Also fix a bug where the return value of
SetErrorHandlerwas used to judge if the error handler was installed. But the return value of that function is the previous signal handler. So there is no need to even store that value.
TFileCheckeras not thread-safe.
- Remove unnecessary mutable in `TAuxVectorFactory.
TDestructorRegistrysingletons as thread-safe as all methods use mutexes.
- Simplify singleton creation in