add_entry is called by (defcustom, defun, defvar) and adds the entry to a list ref, for later use by update_emacs_with_entries.
val update_emacs_with_entries : chop_prefix:string->in_dir:string-> unit
update_emacs_with_entries updates load-history with the information supplied to add_entry, which make it possible to, within Emacs, jump from a symbol defined by Ecaml to the Ecaml source. Each source-file name is adjusted by: