Fix documentation build on centos6

Change-Id: I813c4f063380764b1a4dc069f949a501ed5f0902
Merge commit 'refs/changes/27/427/1' of http://gerrit.tuleap.net/tuleap into tuleap-stable-master

* http://gerrit.tuleap.net/tuleap:
  Fix documentation build on centos6

Change-Id: Ia05d50bb8eb63b0e171cb20845dcb5dd78520f07
Tuleap 5.12.99.71

Change-Id: I7c4af8036ae2d3a5151239b8792ad229f1bd1025
Merge branch 'master' of tuleap.net:tuleap/tuleap/stable into tuleap-stable-master
Tuleap 5.12.99.72

Change-Id: I1a37bbb78d19f64f4e1d240422935c821357b620