Update the analysis releases to LCG_91, 1.0 branch (2017.12.07.)

Finally spent some time on it, and updated the AnalysisBaseExternals and AthAnalysisExternals projects to use LCG_91. This was desperately needed to once again be able to compile the standalone analysis release out of the box on macOS. (See https://sft.its.cern.ch/jira/browse/ROOT-9115 for a description how I wasn't able to get ROOT v6-08-06 working with the latest Apple clang version.)

Unfortunately even v6-10-08 doesn't build out of the box with the very latest clang version. (In C++14 mode.) 😛 So I'm applying the same patch by hand that was already put into the ROOT git repository. (https://github.com/root-project/root/pull/1220)

Looking at the full list of changes between LCG_88 and LCG_91 (http://lcginfo.cern.ch/compare/91/88), I only saw Boost as another thing that

• we build ourselves for the standalone release;
• got updated.

So I updated that one as well.

@krumnack, @will, you'll probably be interested in this.