bug#20365: 24.5; all-completions returns duplicates for Info-read-node-name-1

[Stefan Monnier]

> What I think is happening there is that Info calls
> `completing-read-function' and ultimately gives it (through
> all-completions) a list like '("org" "emacs"...).  And then it expects
> the answer to be in the form "(org)" or "(emacs)".  Which I think is
> strange.

IIUC the problem is as follows: the completion-table used by "g" in
Info-mode lets you complete node names in the current file or lets you
complete file names (which are placed within parens), but the completion
table itself does not add those parens [ A long standing missing feature
here is that it doesn't know how to complete a node name after the
"(<file>)", even though it's a very much valid input to provide.  ]

Your ivy-mode generally wants to have a list of strings as candidates
and wants those strings to be valid return values, whereas the way
completion tables are defined there is no guarantee that you can get
that kind of info from the completion table.

We could change the Info-mode completion table so as to include the
closing paren in the output of `all-completions' (and probably include
the opening paren as well, in that case).  Note also that on my system
"g (ema TAB" includes things like "emacs23/" where "(emacs23/)" is not
a valid element (since emacs-23 is a directorym which is complete in
steps, just as in C-x C-f).


        Stefan