Ftw-solr

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- Fix to_iso8601 prevent rounding errors with DateTime milliseconds above 999500. [deiferni]
- Fix blob extraction for DX items. [mbaechtold]

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- Fix to_iso8601 for years before 1900.
[deiferni]

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- Add support for uploading blobs to extract handler.
[lgraf]

- Add support for Plone 5.0 and 5.1.
[buchi]

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- Add console script for maintenance tasks.
[buchi]

- Add registry setting for enabling/disabling indexing.
[buchi]

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- Avoid sending atomic update commands with null-documents. [lgraf]

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- Fix 'path_depth' indexing handling, when 'path_depth' is not part of the schema. [phgross]