argument query for new choice of help mode.
(info-lookup-symbol): Use it.
(info-lookup-file): Ditto.
(info-lookup): Don't switch to other window, if already in Info buffer.
Removed Info-lookup minor mode.
(info-lookup-file-name-alist): New variable.
(info-lookup-select-mode): New function. Select help mode
according to info-lookup-file-name-alist or fall back to the
buffer's major mode.
(info-lookup): Use info-lookup-select-mode.
(info-lookup-interactive-arguments): Likewise.
(info-complete-symbol): Likewise.
(info-complete-file): Likewise.
(info-complete): Likewise.
(info-lookup->mode-cache, info-lookup->initialized): Likewise.
(info-lookup->completions, info-lookup->refer-modes): Likewise.
(info-lookup->all-modes): Likewise.
(info-lookup-quick-all-modes): New function.
(info-complete): Find the symbol to complete first,
then compute list of completions.
(lisp-mode): Add info-lookup-maybe-add-help for it.
(info-lookup-minor-mode, turn-on-info-lookup):
Added minor mode interface.
(info-lookup-minor-mode-string): New variable.
(info-lookup-minor-mode-map): New variable.
Provide a work-around if the custom library is not available.
(info-lookup-other-window-flag)
(info-lookup-highlight-face): Variables customized.
(info-lookup-alist): No longer customizable.
(info-lookup-add-help, info-lookup-maybe-add-help): Interface
functions for adding new modes.
(info-lookup-add-help*): New function.
(info-lookup-symbol-alist, info-lookup-file-alist): Variables deleted.
This info is specified now by calling info-lookup-maybe-add-help
and info-lookup-add-help.
or if initial guess is already ambiguous.
(info-look-completion): New variable.
(info-lookup-symbol-alist):
Added support for latex-mode, perl-mode, awk-mode, emacs-lisp-mode.
(info-lookup-make-completions): Catch errors one file at a time.
Use a special temp buffer, not the usual info buffer,
and never display it in a window.
