Have "make release" check other release preconditions

As documented in the release instructions in README.md.

Author: EliahKagan

Makefile

@@ -7,13 +7,29 @@ clean:
 	rm -rf build/ dist/ .eggs/ .tox/
 
 release: clean
-	# Check if latest tag is the current head we're releasing
-	@config_opts="$$(printf ' -c versionsort.suffix=-%s' alpha beta pre rc RC)" && \
+	# Check that VERSION and changes.rst exist and have no uncommitted changes
+	test -f VERSION
+	test -f doc/source/changes.rst
+	git status -s VERSION doc/source/changes.rst
+	@test -z "$$(git status -s VERSION doc/source/changes.rst)"
+
+	# Check that ALL changes are commited (can comment out if absolutely necessary)
+	git status -s
+	@test -z "$$(git status -s)"
+
+	# Check that latest tag matches version and is the current head we're releasing
+	@version_file="$$(cat VERSION)" && \
+	changes_file="$$(awk '/^[0-9]/ {print $$0; exit}' doc/source/changes.rst)" && \
+	config_opts="$$(printf ' -c versionsort.suffix=-%s' alpha beta pre rc RC)" && \
 	latest_tag=$$(git $$config_opts tag -l '[0-9]*' --sort=-v:refname | head -n1) && \
 	head_sha=$$(git rev-parse HEAD) latest_tag_sha=$$(git rev-parse "$$latest_tag") && \
-	printf '%-14s = %s\n' 'Latest tag'     "$$latest_tag" \
+	printf '%-14s = %s\n' 'VERSION file'   "$$version_file" \
+	                      'changes.rst'    "$$changes_file" \
+	                      'Latest tag'     "$$latest_tag" \
 	                      'HEAD SHA'       "$$head_sha" \
 	                      'Latest tag SHA' "$$latest_tag_sha" && \
+	test "$$version_file" = "$$changes_file" && \
+	test "$$latest_tag" = "$$version_file" && \
 	test "$$head_sha" = "$$latest_tag_sha"
 
 	make force_release