Added _version_ field definition

This allows the config.xml generated with Haystack’s `build_solr_schema` command to work out-of-the-box with the “example” server in the Solr 4.2.0 distribution.

See http://wiki.apache.org/solr/SolrCloud#Required_Config for details.
Basic support for Polygon fields & queries

* PolygonField is only known to work
    with Solr 4.3+
* PolygonField is currently limited to
    rectangles to prevent the need for
    additional Solr libraries
* PolygonField internally uses Solr
    4.3's geohashing-style field
* SearchQuerySet now has a contains
    method to do point-in-polygon
    filtering, but there is no input
    validation whatsoever
Updated README & index.
Reset backend state when deleting index

Reset setup_complete and existing_mapping when an index is
deleted. This ensures create_index is called later to restore
the settings properly.
Added haystack-rqueue to "Other Apps".
Updated the backend support docs. Thanks to kezabelle & dimiro1 for the report!
Updated description for TIMEOUT setting
Merge pull request #810 from pabluk/minor-docs-fix

Updated description for TIMEOUT setting - thanks @pabluk
Merge remote-tracking branch 'infoxchange/fix-elasticsearch-index-settings-reset' into HEAD
Merge remote-tracking branch 'toastdriven/master' into HEAD
[elasticsearch] Initial work on supporting geo_shapes
[elasticsearch] Support geo_shape bounding box field and query
Merge remote-tracking branch 'origin/master'