refactor(esup.el): change loop to cl-loop
refactor(esup-last-result-start-point):  avoid free variable
docs(esup-server-process): use complete sentences
docs(esup.el): clarify doc string
refactro(esup-server-log): change string-empty-p to string-equal
refactor: require cl-lib all the time

We need functions from cl-seq as well as the cl-loop macro.