Add more checks to makefile

We're trying to prevent clobbering other's changes or forgetting to push
ours.

Makefile

@@ -10,12 +10,27 @@ sign: $(patsubst %,%.sig,$(wildcard *.zone))
 
 .PHONY: check-clean
 check-clean:
-	[ ! -e .git ] || git diff-index --exit-code HEAD
-	[ ! -e .git ] || \
-		git ls-files --other --directory --exclude-standard | \
-		sed -n '/.*\.zone/{p;q1}'
-
-upload:
+	@git diff-index --exit-code HEAD >/dev/null && \
+	git ls-files --other --directory --exclude-standard | \
+		sed -n '/.*\.zone/{p;q1}' || { \
+	printf 'Commit your changes before uploading!\n' >&2; \
+	git status -s; exit 1; }
+
+GIT_BRANCH=$(shell git name-rev --name-only HEAD)
+GIT_BRANCH_REMOTE=$(shell git config branch.$(GIT_BRANCH).remote)
+GIT_BRANCH_MERGE=$(shell git config branch.$(GIT_BRANCH).merge) # remote branch
+.PHONY: fetch
+check-uptodate: FORCE
+	git fetch $(GIT_BRANCH_REMOTE) $(GIT_BRANCH_MERGE)
+	@[ -z "`git rev-list -n1 HEAD@{upstream} --not HEAD`" ] || { \
+		printf 'Unpulled changes, refusing to upload zones!\n' >&2; \
+		git log --decorate --oneline --graph -n3 \
+			HEAD@{upstream} --not HEAD; \
+	}
+
+.PHONY: upload
+upload: check-clean check-uptodate
+upload: sign
 	printf 'put %s\n' *.zone *.sig | \
 		sftp $(SFTP_FLAGS) zones@ns0.it-syndikat.org:zones/