Cherry-pick "Merge branch 'Ubuntu1710Fixes-1.0-20180214' into '1.0'" into master

Ubuntu-17.10 Fixes, 1.0 branch (2018.02.15.)

See merge request !240 (merged)

(cherry picked from commit 655f3dbc)

• c90f5fe2 Disabled treating "array-bounds" warnings as errors with GCC 7, since
• 9c630fa2 Only realised now that XRootD is building some of its code against
• 5c1cb66a Merge remote-tracking branch 'upstream/1.0' into Ubuntu1710Fixes-1.0-20180214
• 97274b8a Modified the Python detection code in AnalysisBaseExternals to allow