initrd/init:find_save_file() - tahrpup LN#713-740

# LN# 713 to 740 of /initrd/init (tahrpup) - http://www.pearltrees.com/s243a/initrd-init/id19535893/item224274990
# LN# 765 to 800 https://github.com/puppylinux-woof-CE/woof-CE/blob/c96d661c2232caef1d69c693de673fb0e54796f8/initrd-progs/0initrd/init#L765
find_save_file() {
# "$1" - mount point - ex:  /mnt/pdrv
# "$2" - partition name - ex: sdb2
# "$3" - file system type - ex: ext4
 if [ "$SAVE_BP_DIR" ];then
  SAVE_DIR="$SAVE_BP_DIR"
 else
  SAVE_DIR="${PSUBDIR}/"
 fi
 SAVE_FILES="$(ls -d ${1}${SAVE_DIR}${DISTRO_FILE_PREFIX}save* 2>/dev/null)"
 for ONE_SAVE in $SAVE_FILES;do
  #validate savefiles here
  [ "$ONE_FS_IS_LINUX" != "yes" ] && [ -d "$ONE_SAVE" ] && continue
  IS_OK=""
  case $ONE_SAVE in
   *.2fs|*.3fs|*.4fs) [ -s "$ONE_SAVE" ] && IS_OK="yes" ;;
   *.BKP-*) IS_OK="$PSAVEBKP" ;; #written by /usr/sbin/pupsave-backup
   *) [ -d "$ONE_SAVE" ] && IS_OK="yes" ;;
  esac
  [ "$IS_OK" ] && PUP_SAVES="${PUP_SAVES}${2},${3},${SAVE_DIR}$(basename $ONE_SAVE)
"
 done
 PUP_SAVES="$(echo "$PUP_SAVES")" #remove trailing newline char
 echo "MENU_MAX_PUPSAVES=${MENU_MAX_PUPSAVES}" #debug
 if [ "$MENU_MAX_PUPSAVES" ] ; then
   PUP_SAVES="$(echo "$PUP_SAVES" | head -n $MENU_MAX_PUPSAVES)"
 fi
}