v4 of DB_RETRY_LOCK patches

[Tomi Ollila]

On Sun, Jun 26 2016, David Bremner <david at tethera.net> wrote:

> This obsoletes
>
>    id:1465043356-23420-2-git-send-email-david at tethera.net
>
> I investigated adding a timeout (including talking a bit to Xapian
> upstream about it), and thought about some runtime configuration
> options, but for now I settled on a configure. Depending what
> experiences people report, we would make the default disabled for the
> next release.

Looks good, tests pass (*)

Tomi

I.e.

 missing prerequisites: lock retry support
  SKIP   all tests in T620-lock