added priority support for cluster state updates:

 * URGENT:
    * cluster_reroute (api)
    * refresh-mapping
    * cluster_update_settings
    * reroute_after_cluster_update_settings
    * create-index
    * delete-index
    * index-aliases
    * remove-index-template
    * create-index-template
    * update-mapping
    * remove-mapping
    * put-mapping
    * open-index
    * close-index
    * update-settings

* HIGH
    * routing-table-updater
    * zen-disco-node_left
    * zen-disco-master_failed
    * shard-failed
    * shard-started

* NORMAL
    * all other actions
fixed a bug in PrioritizedThreadPoolExecutor:

now execute(Runnable) verifies the command is added as PrioritizedRunnable
fixed a bug in PrioritizedThreadPoolExecutor:

now execute(Runnable) verifies the command is added as Comparable
fixed a bug in PrioritizedThreadPoolExecutor:

now execute(Runnable) satisfies the priority and fifo nature of same-priority runnables
Fix filter cache stats calculation

Fixes #2609
added norwegian minimal stemmer
Also support camel case notation for minimal norwegian.
Index with no replicas might loose on going documents while relocating a shard
fixes #26421
# Rescore Feature

The rescore feature allows te rescore a document returned by a query based
on a secondary algorithm. Rescoring is commonly used if a scoring algorithm
is too costly to be executed across the entire document set but efficient enough
to be executed on the Top-K documents scored by a faster retrieval method. Rescoring
can help to improve precision by reordering a larger Top-K window than actually
returned to the user. Typically is it executed on a window between 100 and 500 documents
while the actual result window requested by the user remains the same.

# Query Rescorer

The `query` rescorer executes a secondary query only on the Top-K results of the actual
user query and rescores the documents based on a linear combination of the user query's score
and the score of the `rescore_query`. This allows to execute any exposed query as a
`rescore_query` and supports a `query_weight` as well as a `rescore_query_weight` to weight the
factors of the linear combination.

# Rescore API

The `rescore` request is defined along side the query part in the json request:

```json
curl -s -XPOST 'localhost:9200/_search' -d {
  "query" : {
    "match" : {
      "field1" : {
        "query" : "the quick brown",
        "type" : "boolean",
        "operator" : "OR"
      }
    }
  },
  "rescore" : {
    "window_size" : 50,
    "query" : {
      "rescore_query" : {
        "match" : {
          "field1" : {
            "query" : "the quick brown",
            "type" : "phrase",
            "slop" : 2
          }
        }
      },
      "query_weight" : 0.7,
      "rescore_query_weight" : 1.2
    }
  }
}
```

Each `rescore` request is executed on a per-shard basis within the same roundtrip. Currently the rescore API
has only one implementation (the `query` rescorer) which modifies the result set in-place. Future developments
could include dedicated rescore results if needed by the implemenation ie. a pair-wise reranker.
*Note:* Only regualr queries are rescored, if the search type is set to `scan` or `count` rescorers are not executed.

Closes #2640
Bulk execution while a shard is replication might send erroneous version conflict failures for certain items
fixes #2642
delete indices before running the tests
Added `sort_mode` option that defines what value to pick in the case the sort field is multi-valued.

The `min` and `max` sort modes are supported for all field types. Either the lowest value or the highest value is picked. In addition to that number based fields also support `sum` and `avg` as sort mode. If `sum` sort mode is used then all the values for a field and belonging to a document are added together and the result of that is used as sort value. If the `avg` sort mode is used then the average of all values for the sort field belonging to that document is used as sort value.

Relates to #2634
add increased timeout waiting for relocation when running on small boxes
Added more trace logging related to finding master.
possibly incorrect use of Lucene OneMerge.totalBytesSize
fixes #2643
Let the update index settings action fail if non dynamic settings are changed for open indices.
Closes #2647
updating non dynamic settings throws an error now
Warmers do not load field data cache for sorting on new segments
fixes #2649
delay reroute only after we publish that a shard has started
Optimize conversion to a cacheable DocIdSet