Do not diagnose lookup problems in lookup() interfaces.
Remove global for constructor lists shared in TMetaUtils and rootcling

and opt for a percolation of arguments.
The collection of constructors is not anymore a vector but a list.
Add the text editor
Recurse over bases when looking for a method. Fixes db074c4e. (ROOT-5738)
Add a protection for creating the Minimizer and DistSampler  with the plugin manager in multithreads
(thanks for Andreas, see ROOT-5335)
Fix also the DistSampler
Make use of TEnumConstant, accelerating Init() (ROOT-5476).