Utilities/Sphinx: Port cmake extension to Sphinx 1.4

Sphinx 1.4 introduced a breaking change to `indexnode` by changing
the length of a tuple.  Teach our extension to produce a tuple of
the proper length for the version of Sphinx in use.

This gets rid of the "4 column based index found" warning.
2 jobs for sphinx-indexnode
Status Name Job ID Coverage
passed ghostflow-branch-check

passed ghostflow-commit-check