Fix quilt tests so that they are always done in the same order and
therefore generate test results that we can successfully compare
against a master test results file.

GNU make v3.82 introduced a change that caused this failure:

  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.

The upstream developers are aware of this problem and provided the suggested
change here.

--- Makefile.in.orig	2015-01-16 13:06:24.023825051 -0800
+++ Makefile.in	2015-01-16 13:07:09.572752077 -0800
@@ -119,7 +119,8 @@
 
 GIT_DESC :=	$(shell ./git-desc | sed -e 's:^v::')
 
-TESTS :=	$(filter-out test/patch-wrapper.test,$(wildcard test/*.test))
+# Tests are sorted to make it easier to compare the results between runs
+TESTS :=	$(filter-out test/patch-wrapper.test,$(sort $(wildcard test/*.test)))
 DIRT +=		test/.depend $(wildcard test/.*.ok)
 
 # Settings for running the uninstalled version of quilt in the source tree: