bug#16260: 24.3.50; shell-command-completion and removal of exec-directory from exec-path

[Eli Zaretskii <eliz@gnu.org>]

shell--command-completion-data has this FIXME comment:

  (defun shell--command-completion-data ()
    "Return the completion data for the command at point."
    (let* ((filename (or (comint-match-partial-filename) ""))
	   (start (if (zerop (length filename)) (point) (match-beginning 0)))
	   (end (if (zerop (length filename)) (point) (match-end 0)))
	   (filenondir (file-name-nondirectory filename))
	   (path-dirs (cdr (reverse exec-path))) ;FIXME: Why `cdr'?

As Jarek pointed out in his patch for bug #15461, the doc string of
shell-dynamic-complete-command hints on the reason:

  This function is similar to `comint-dynamic-complete-filename', except that it
  searches `exec-path' (minus the trailing Emacs library path) for completion
  candidates.           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

It talks about "Emacs library path", but actually means the libexec
directory, which is normally the value of exec-directory.

However, just clipping away the last member of exec-path list only
does TRT in the default case.  It will not work if either of the
following happens:

  . The user changes epaths.h to specify more than a single directory

  . EMACSPATH is set in the environment

To get this right, we should record at startup time the value of
exec-path before appending $PATH to it, and then filter out the
directories recorded at that time in shell--command-completion-data.

As a minor nit, the doc string of shell-dynamic-complete-command
should not talk about "library path", which is a non-existing term in
Emacs, but instead mention exec-directory.


In GNU Emacs 24.3.50.187 (i686-pc-mingw32)
 of 2013-12-26 on HOME-C4E4A596F7
Bzr revision: 115758 fgallina@gnu.org-20131226164519-xccapciswuo6gvid
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --prefix=/d/usr --enable-checking=yes,glyphs 'CFLAGS=-O0
 -gdwarf-2 -g3''

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

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  tooltip-mode: t
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  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

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