bug#27624: Implement Info-number-index-items

[積丹尼 Dan Jacobson]

Don't you think it is weird for an Info page to say

  5.17 Android shell setup hints
  ==============================

but then in its parent index, one only sees

  Configuring TRAMP for use

  * Remote shell setup::          Remote shell setup hints.
  * Android shell setup::         Android shell setup hints.
  * Auto-save and Backup::        Auto-save and Backup.

Therefore I hereby propose there be created

  (defcustom Info-number-index-items 'full
    "'basic means to put the subsection number in front of index items.
    'full means to put the full index number in front of index items...

Thus one could see

  5 Configuring TRAMP for use

  * 16 Remote shell setup::          Remote shell setup hints.
  * 17 Android shell setup::         Android shell setup hints.
  * 18 Auto-save and Backup::        Auto-save and Backup.

Or

  5 Configuring TRAMP for use

  * 5.16 Remote shell setup::          Remote shell setup hints.
  * 5.17 Android shell setup::         Android shell setup hints.
  * 5.18 Auto-save and Backup::        Auto-save and Backup.

In fact, I can't think of any book or online document that doesn't
number their chapters or indexes.