[PATCH v2] build: drop support for xapian versions less than 1.4

[David Bremner]

Tomi Ollila <tomi.ollila at iki.fi> writes:

> Xapian 1.4 is over 3 years old now (1.4.0 released 2016-06-24),
> and 1.2 has been deprecated in Notmuch version 0.27 (2018-06-13).
>
> Xapian 1.4 supports compaction, field processors and retry locking;
> conditionals checking compaction and field processors were removed
> but user may want to disable retry locking at configure time so it
> is kept.

pushed, thanks.

Now somewhere I have patches for compatibility with xapian 1.5 that I
think was blocked on that...

d