[ccache/el6] (4 commits) ...Merge branch 'master' into el6

[Ville Skyttä]

Summary of changes:

  754dbc4... Update to 3.1.5. (*)
  f443a74... Update to 3.1.6. (*)
  98ad636... Turn on CCACHE_HASHDIR by default (#759592, Jan Kratochvil) (*)
  6d987f1... Merge branch 'master' into el6

(*) This commit already existed in another branch; no separate mail sent