Make the loaddefs scraping compilation output look more regular

Make the loaddefs scraping compilation output look more regular

* lisp/Makefile.in ($(lisp)/loaddefs.el): Don't output the
directories here.

* lisp/emacs-lisp/autoload.el (batch-update-autoloads--summary):
New function.
(batch-update-autoloads): Use it to output the directories we're
scraping.

This changes the compilation output from:

Directories for loaddefs: . ./calc ./calendar ./cedet ./cedet/ede
./cedet/semantic ./cedet/semantic/analyze ./cedet/semantic/bovine
./cedet/semantic/decorate ./cedet/semantic/symref ./cedet/semantic/wisent
./cedet/srecode ./emacs-lisp ./emulation ./erc ./eshell ./gnus ./image
./international ./language ./leim ./leim/ja-dic ./leim/quail ./mail ./mh-e
./net ./nxml ./org ./play ./progmodes ./textmodes ./url ./vc

(but all on one long line)

To:

  SCRAPE   . ./calc ./calendar ./cedet ./cedet/ede ./cedet/semantic
  SCRAPE   ./cedet/semantic/analyze ./cedet/semantic/bovine
  SCRAPE   ./cedet/semantic/decorate ./cedet/semantic/symref
  SCRAPE   ./cedet/semantic/wisent ./cedet/srecode ./emacs-lisp ./emulation
  SCRAPE   ./erc ./eshell ./gnus ./image ./international ./language ./leim
  SCRAPE   ./leim/ja-dic ./leim/quail ./mail ./mh-e ./net ./nxml ./org ./play
  SCRAPE   ./progmodes ./textmodes ./url ./vc

Compilation output with very long lines can be mistaken for errors
when they scroll by fast in the compilation output.  Making it look
more like normal informational output avoids this confusion.