bug#158: Etags completion problem for local tags table

[Josiah Schwab <jschwab@gmail.com>]

Hello,

> It doesn't sound hard to test for someone who does have emacs 25
> built.

I have been able to reproduce this bug under emacs 25.1 and git master
(at c542fab).  Here are the steps to reproduce.

For simplicity, I am using two very minimal tags files (fruits/TAGS and
vegetables/TAGS) available from

  https://github.com/jschwab/emacs-tags-issues

but any tags files ought to do.

Open emacs with emacs -Q

Do
,----
| C-x C-f file1
| M-: (visit-tags-table "fruits/TAGS")
| M-. [TAB]
`----

The possible completions offered will be fruits, as expected.

Continue by doing
,----
| C-x C-f file2
| M-: (visit-tags-table "vegetables/TAGS" t)
`----

The user is prompted, "Keep current list of tags tables also? (y or
n)".  Reply n.

Now do
,----
| M-. [TAB]
`----

The possible completions offered will be fruits and not vegetables as
expected.

After this, the *Messages* buffer looks like
,----
| (New file)
| Starting a new list of tags tables
| "/home/jschwab/Software/emacs-tags-issues/fruits/TAGS"
| Making tags completion table for /home/jschwab/Software/emacs-tags-issues/fruits/TAGS...done
| Making completion list...
| Quit
| (New file)
| Keep current list of tags tables also? (y or n) n
| Starting a new list of tags tables
| "/home/jschwab/Software/emacs-tags-issues/vegetables/TAGS"
| Making tags completion table for /home/jschwab/Software/emacs-tags-issues/vegetables/TAGS...
| Making tags completion table for /home/jschwab/Software/emacs-tags-issues/fruits/TAGS...
| Making tags completion table for /home/jschwab/Software/emacs-tags-issues/vegetables/TAGS...done
| Making completion list...
| Quit
`----

It seems like this issue could be related to

  https://debbugs.gnu.org/cgi/bugreport.cgi?bug=19741

Josiah