add MockPageCacheRecycler in test jar

MockPageCacheRecycler is missing in test jar which makes failing tests when using
test jar in plugins:

```
1> [2014-01-11 10:51:30,531][ERROR][test                     ] FAILURE  : testWikipediaRiver(org.elasticsearch.river.wikipedia.WikipediaRiverTest)
  1> REPRODUCE WITH  : mvn test -Dtests.seed=5DAFD4FBAE587363 -Dtests.class=org.elasticsearch.river.wikipedia.WikipediaRiverTest -Dtests.method=testWikipediaRiver -Dtests.prefix=tests -Dtests.network=true -Dfile.encoding=MacRoman -Duser.timezone=Europe/Paris -Des.logger.level=INFO -Des.node.local=true -Dtests.cluster_seed=134842C2D806FFC0
  1> Throwable:
  1> java.lang.NoClassDefFoundError: org/elasticsearch/cache/recycler/MockPageCacheRecycler
  1>     org.elasticsearch.test.cache.recycler.MockPageCacheRecyclerModule.configure(MockPageCacheRecyclerModule.java:30)
  1>     org.elasticsearch.common.inject.AbstractModule.configure(AbstractModule.java:60)
```

Closes #4694.
Replaced the multi-field type in favour for the multi fields option that can be set on any core field.

When upgrading to ES 1.0 the existing mappings with a multi-field type automatically get replaced to a core field with the new `fields` option.

If a `multi_field` type-ed field doesn't have a main / default field, a default field will be chosen for the multi fields syntax. The new main field type
will be equal to the first `multi_field` fields' field or type string if no fields have been configured for the `multi_field` field and in both cases
the default index will not be indexed (`index=no` is set on the default field).

If a `multi_field` typed field has a default field, that field will replace the `multi_field` typed field.

Closes to #4521
Add new option `min_doc_count` to terms and histogram aggregations.

`min_doc_count` is the minimum number of hits that a term or histogram key
should match in order to appear in the response.

`min_doc_count=0` replaces `compute_empty_buckets` for histograms and will
behave exactly like facets' `all_terms=true` for terms aggregations.

Close #4662
Fix YAML in test/indices.open/20_multiple_indices.yaml