Add a Makefile to build an SQLite-compatible schema

Allow for automatically converting the schema into a schema that works
with SQLite by running `make` from the schema/ subdirectory. Use the new
Makefile in the test suite.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>

schema/Makefile

@@ -0,0 +1,11 @@
+aur-schema-sqlite.sql: aur-schema.sql
+	sed \
+		-e 's/ ENGINE = InnoDB//' \
+		-e 's/ [A-Z]* UNSIGNED NOT NULL AUTO_INCREMENT/ INTEGER NOT NULL/' \
+		-e 's/([0-9, ]*) UNSIGNED / UNSIGNED /' \
+		$< >$@
+
+clean:
+	rm -rf aur-schema-sqlite.sql
+
+.PHONY: clean