use the file size to detect file modification
use the file size to detect file modification

Signed-off-by: Arseniy Alekseyev <81716b89e7c53c56e819cd55a9370136d1adf7d1@janestreet.com>

dra27/jbuilder,janestreet/jbuilder,dra27/jbuilder,dra27/jbuilder,janestreet/jbuilder,janestreet/jbuilder,janestreet/jbuilder,dra27/jbuilder,janestreet/jbuilder,dra27/jbuilder,dra27/jbuilder,janestreet/jbuilder