Always export source tarballs

- If a package has an increased Debian revision (e.g. 1.0-1 -> 1.0-2),
dpkg-genchanges is very smart and won't re-export the original source
tarball. Override this behavior by adding -sa to debbuildopts. For a
binary-only package, this has no effect.

Change-Id: I30d79ae306bb5ad8998b9aa4a8fba3009223c22b
diff --git a/packages.mk b/packages.mk
index 67ef924..39746eb 100644
--- a/packages.mk
+++ b/packages.mk
@@ -90,7 +90,7 @@
 	$(LOG) $1 pbuilder pdebuild
 	cd $(PRODUCT_OUT)/obj/$1; pdebuild \
 		--buildresult $(PRODUCT_OUT)/packages/$(if $6,$6,core) -- \
-		--debbuildopts "--build=$(if $5,$5,full)" \
+		--debbuildopts "--build=$(if $5,$5,full) -sa" \
 		--basetgz $(ROOTDIR)/cache/base.tgz \
 		--configfile $(ROOTDIR)/build/pbuilderrc \
 		--hookdir $(ROOTDIR)/build/pbuilder-hooks \