swcarpentry/bc — pull request #322 by r-gaia-cs (2014-02-17 16:48:02+00:00)
Title: Fix problem with book "timeline"

From [GNU Make 3.82 release](https://lists.gnu.org/archive/html/info-gnu/2010-07/msg00023.html)

> * WARNING: Future backward-incompatibility!
>
> Wildcards are not documented as returning sorted values, but up to and
including this release the results have been sorted and some makefiles are
apparently depending on that. In the next release of GNU make, for
performance reasons, we may remove that sorting. If your makefiles
require sorted results from wildcard expansions, use the $(sort ...)
function to request it explicitly.

This PR changes `Makefile` to make it compatible with GNU Make >= 3.82.