Merge branch 'LCGNightlySetup-20170412' into 'master'

Enabling builds against LCG nightlies, master branch (2017.04.12.)

See merge request !930

Projects/AnalysisBase/externals.txt

 # Versions of the various externals to build before starting the build of
 # this project, when doing a full stack nightly build.
 
-AnalysisBaseExternalsVersion = 061e4f81
+AnalysisBaseExternalsVersion = 6491b6ae

Projects/Athena/externals.txt

@@ -5,5 +5,5 @@
 # an "origin/" prefix before it. For tags however this is explicitly
 # forbidden.
 
-AthenaExternalsVersion = 061e4f81
+AthenaExternalsVersion = 6491b6ae
 GaudiVersion = v28r1.conditions.010