Log Message:
Update to 1.4.7. From the changelog:

API:

* Database::check(): Fix bogus error reports for documents with length zero
  due to a new check added in 1.4.6 that the doclength was between the stored
  upper and lower bounds, which failed to allow for the lower bound ignoring
  documents with length zero (since documents indexed only by boolean terms
  aren't involved in weighted searches).  Reported by David Bremner.

* Query: Use of Query::MatchAll in multithreaded code causes problems because
  the reference counting gets messed up by concurrent updates.  Document that
  Query(string()) should be used instead of MatchAll in multithreaded code, and
  avoid using it in library code.  Reported by Germán M. Bravo.

* Stem:

  + Stemming algorithms added for Irish, Lithuanian, Nepali and Tamil.

  + Merge Snowball compiler changes which improve code generation.

  + Merge optimisations to the Arabic and Turkish stemmers.

glass backend:

* A long-lived cursor on a table in a WritableDatabase could get into
  an invalid state, which typically resulted in a DatabaseCorruptError
  being thrown with the message:

      Db block overwritten - are there multiple writers?

  But in fact the on-disk database is not corrupted - it's just that
  the cursor in memory has got into an inconsistent state.  It looks
  like we'll always detect the inconsistency before it can cause on-disk
  corruption but it's hard to be completely certain.

  The bug is in code to rebuild the cursor when the underlying table
  changes in ways which require that, which is a fairly rare occurrence
  to start with, and only triggers when a block in the cursor has been
  released, reallocated, and we tried to load it in the cursor at the
  same level - the cursor wrongly assumes it has the current version
  of the block.

  Reported with a reproducer by Sylvain Taverne.  Confirmed by David
  Bremner as also fixing a problem in notmuch for which he hadn't managed
  to find a reduced reproducer.