lib/scripts/fileident

adding subsection about the predicate compiler to the code generator tutorial

#!/usr/bin/env bash
#
# fileident --- produce file identification based

FILE="$1"

if [ -n "$ISABELLE_FILE_IDENT" -a -f "$FILE" -a -r "$FILE" ]
then
  ID=$(cat "$FILE" | $ISABELLE_FILE_IDENT | cut -d " " -f 1) && echo -n "$ID"
fi