lazycatd.scm: Rename request handlers.

* lazycat-daemon/lazycatd.scm
  (lazycat-stop): Rename to `handle-stop-req'.
  (lazycat-add): Rename to `handle-add-req'.
  (lazycat-rem): Rename to `handle-rem-req'.
  (lazycat-list): Rename to `handle-list-req'.
  (lazycat-get): Rename to `handle-get-req'.
  (lazycat-set): Rename to `handle-set-req'.
  (lazycat-exec): Rename to `handle-exec-req'.
  (lazycat-diff): Rename to `handle-diff-req'.
  (main-loop): Update calls to request handlers.