Ftw-solr

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- Use Solr Cell only for text extraction. The SearchableText is now also indexed
using the update handler which allows atomic updates. Also fixes 137.
[buchi]

- Fix error when trying to delete an object without a unique key. [jone]

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- Make sure to always update 'path_depth' if 'path' is (re)indexed.
[lgraf]

- Handle facet_counts in solr response.
[njohner]

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- Perform soft commits and wait for new searcher by default to allow near real
time (NRT) searching.
[buchi]

- Additionaly index metadata of files using an update command to make them
visible as soon as possible.
[buchi]

- Flush optimize command.
[buchi]

- Add support for indexing path depth.
[buchi]

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- Fix partial reindexing (atomic updates) for fields without a value.
[buchi]

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- Fix reindexObjectSecurity patch to account for special handling of system
roles in allowedRolesAndUsers indexer.
[lgraf]

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- Patch reindexObjectSecurity to optimize indexing of large trees.
[lgraf]

- Fix diff for items with a modification date that has no fractional seconds.
[buchi]

- Provide an error message when raising an AttributeError in SolrDocument.
[buchi]