git submodule support

bin/gbuild

@@ -284,6 +284,7 @@ build_desc["remotes"].each do |remote|
   commit = `cd inputs/#{dir} && git log --format=%H -1 #{commit}`.strip
   raise "error looking up commit for tag #{remote["commit"]}" unless $?.exitstatus == 0
   system!("cd inputs/#{dir} && git checkout -q #{commit}")
+  system!("cd inputs/#{dir} && git submodule update --init --recursive --force")
   in_sums << "git:#{commit} #{dir}"
 end