bug#24750: 26.0.50; incorrect Edebug spec for cl-loop

[Gemini Lasswell]

The Edebug spec for cl-loop is incorrect, causing an error message when
you try to instrument code that uses a cl-loop "using" clause. To
reproduce, starting at the root of the Emacs source tree:

1. emacs -Q
2. C-x C-f lisp/registry.el RET
3. M-x edebug-all-defs RET
4. M-x eval-buffer RET

Result: Bad ‘using’ clause

The error happens during macro expansion of the cl-loop in
registry-search, when it tries to parse a using clause that has
had edebug-before and edebug-after added to it.

I tried adding:

["using" (symbolp symbolp)]

to the debug spec for cl-loop and that seemed to fix the problem.

In GNU Emacs 26.0.50.3 (x86_64-apple-darwin15.6.0, NS appkit-1404.47 Version 
10.11.6 (Build 15G1004))
 of 2016-10-19 built on rainbow.local
Repository revision: 21e8ab1e6cebfb8cf6e628f4dda907749e935820
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
Debug on Error disabled globally
Edebug: initialize-instance [2 times]
Edebug: edebug-anon0
Edebug: registry-lookup
Edebug: registry-lookup-breaks-before-lexbind
Edebug: registry-lookup-secondary
Edebug: registry-lookup-secondary-value
Edebug: registry--match
Edebug: registry-search
Eager macro-expansion failure: (error "Bad ‘using’ clause") [2 times]
cl--parse-loop-clause: Bad ‘using’ clause
Configured using:
 'configure --with-ns --disable-ns-self-contained'

Configured features:
JPEG RSVG IMAGEMAGICK NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS
NS

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
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  smartparens-strict-mode: t
  smartparens-mode: t
  which-key-mode: t
  modalka-mode: t
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  global-auto-revert-mode: t
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  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
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epg gnus-util rmail rmail-loaddefs mailabbrev gmm-utils mailheader debug
eieio-base vc-git diff-mode colir flx dired dired-loaddefs counsel
esh-util swiper ivy delsel ffap edebug ielm pp face-remap guess-style
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Memory information:
((conses 16 518401 171065)
 (symbols 48 40970 0)
 (miscs 40 917 715)
 (strings 32 96687 172176)
 (string-bytes 1 2837074)
 (vectors 16 62598)
 (vector-slots 8 1104571 30962)
 (floats 8 967 957)
 (intervals 56 2552 758)
 (buffers 976 17))