msearch REST API should support source parameter

As stated in documentation, we should support `?source=` parameter in msearch REST operations.

This is how to reproduce it:

```sh
curl -XDELETE "http://localhost:9200/test"

curl -XPOST "http://localhost:9200/test/type/1?refresh" -d'{
    "foo": "bar"
}'

cat requests
{}
{"query" : {"match_all" : {}}}

curl -XGET localhost:9200/_msearch --data-binary @requests

curl -XGET "http://localhost:9200/test/type/_mget?source=%7B%7D%0A%7B%22query%22%3A%7B%22match_all%22%3A%7B%7D%7D%7D%0A"
```

Closes #4901.
percolate REST API should support source parameter

As stated in documentation, we should support `?source=` parameter in percolate REST operations.

This is how to reproduce it:

```sh
curl -XDELETE "http://localhost:9200/test"

curl -XPUT "http://localhost:9200/test/.percolator/1" -d'
{
"query" : {
"match" : {
"foo" : "bar"
}
}
}'

# This one works
curl -XPOST "http://localhost:9200/test/message/_percolate" -d '{
"doc" : {
"foo" : "bar is in foo"
}
}'

# This one gives: BroadcastShardOperationFailedException[[test][2] ]; nested: PercolateException[failed to percolate]; nested: ElasticsearchIllegalArgumentException[Nothing to percolate];
curl -XGET "http://localhost:9200/test/message/_percolate?source=%7B%22doc%22%3A%7B%22foo%22%3A%22bar%20is%20in%20foo%22%7D%7D"
```

Closes #4903.
Upgrade to Lucene 4.6.1

This upgrade includes a fix for RAM estimation on IndexReader
that allows to expose the amount of used bytes per segment now
as a setting in Elasticsearch. (LUCENE-5373)

Additionally this bugfix release contained a small fix for highlighting
that was already ported to Elasticsearch when reported (LUCENE-5361)

Closes #4897
s/lets/let's/
Ignore internal errors if JVM can't find the memory pool
[DOCS] Clarified docs for cluster.routing.allocation.same_shard.host cluster setting

Clarified also javadocs for SameShardAllocationDecider