The configure part is essentially the same as the other checks using
pkg-config. Since the optional inclusion of this feature changes what
options are available to the user, include it in the "built_with"
pseudo-configuration keys.
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.
This flag should make it easier to write the code for session-key
handling.
Note that this only works for GMime 2.6.21 and later (the session key
interface wasn't available before then). It should be fine to build
the rest of notmuch if this functionality isn't available.
Note that this also adds the "session_key" built_with() aspect to
libnotmuch.
C99 stdbool turned 18 this year. There really is no reason to use our
own, except in the library interface for backward
compatibility. Convert the lib internally to stdbool.
This support will be present only if the appropriate version of xapian
is available _and_ the user did not disable the feature when
building. So there really needs to be some way for the user to check.
Many of the external links found in the notmuch source can be resolved
using https instead of http. This changeset addresses as many as i
could find, without touching the e-mail corpus or expected outputs
found in tests.
