[Tracker] Indexer-split branch now requires sqlite 3.5

[Philip Van Hoof <spam pvanhoof be>]

Hi there,

We bumped the version of sqlite to 3.5 in the indexer-split branch
because we require --enable-threadsafe, and 3.4 doesn't guarantee this
(for example for packaged versions of libsqlite3)

If there's a way to determine whether a packaged version has threadsafe
enabled, then we could of course use that as a check too.

-- 
Philip Van Hoof, freelance software developer
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