Add / to the list of characters to escape

This is a fix for migration from elasticsearch 0.20.6 to 0.90+.
Elasticsearch 0.90+ uses Lucene 4.  One change in Lucene 4 from Lucene 3
is that a / character in a query denotes the start of a regular
expression.  We don't want to use regular expressions in our queries, so
add / to the list of characters to escape.  This change fixes the
test_should_not_match_on_slug integration test.

For more information:
https://github.com/elasticsearch/elasticsearch/issues/2980
Merge pull request #221 from alphagov/regex_fix_for_0_90

Add / to the list of characters to escape
Supporting adding non-edition documents from hash.

Uses an optional `_type` parameter in the hash.
Defaults to "edition".
Merge pull request #222 from alphagov/support-adding-non-edition-documents

Supporting adding non-edition documents from hash.
Whitespace.
Support `_id` field in bulk documents.

- Don't assume the `link` field is the ID.
- Keep backwards compatibility if `_id` is not
  present.
Export `_id` and `_type` fields to elasticsearch.

Preserves backwards compatibility.
Merge pull request #223 from alphagov/fix-nonedition-support

Fix nonedition support
Add 'miliband' to ignore list
Stemming override for 'recovery'

Searches for statutory pay such as 'SSP recovery' should match content
about 'recover' or 'recovering'.
Merge pull request #224 from alphagov/suggestions-20140509

Add 'miliband' to ignore list
Synonym updates
Merge pull request #225 from alphagov/synonyms-20140509

Synonym and stemming updates
Add mappings for the page_traffic index
Add a popularity field to the mainstream, government, and detailed guide schemas
Add popularity field to documents when indexing

This field is populated from the page-traffic index, which in turn is
populated from a dump file produced by the python scripts in the
search-analytics repository.

The popularity is currently defined here as 1.0 / the rank of the page
in terms of traffic.  ie, Our highest traffic page gets 1.0, the next
highest gets 0.5, the next highest gets 0.333.  This is a nice and
stable measure.
Use the popularity field when searching
Describe how to include popularity information in the search index.
If there's no query or sort, sort by popularity

Without a query, there's no relevance score, so unless an explicit order
is given the sort order is essentially undefined.  Use the popularity
field in this case to return the most popular items first, because this
is probably useful and almost free to do.
Separate index names into content and auxiliary.

The page-traffic index is an example of an auxiliary index; it doesn't
hold content, but is used outside the main query (in this case, at
indexing time). We'll shortly be adding another such index to hold
best-bets.

Sitemaps should be made only from content indexes.  The search server
needs to know all the allowed names for its validation of index names
when opening indexes.