Add submodule for debtagsd' heuristics from a (temporary github repository).

This will make it easier to track my changes to debtagsd before I submit them
to Enrico for review / advices.

.gitmodules

-[submodule "debexpo/lib/debtagsd"]
-	path = debexpo/lib/debtagsd
-	url = git://anonscm.debian.org/debtags/debtagsd.git
+[submodule "debexpo/lib/debtags_heuristics"]
+	path = debexpo/lib/debtags_heuristics
+	url = git://github.com/clemux/debtags-heuristics.git

debtags_heuristics @ 865992ec

+Subproject commit 865992ec92e7a9b6237adf5ffa08c4e69ad239b3