Fix for #2461 JS driver lost variable digits
Made db_term_t use the cluster_access.databases_semilattice_metadata watchable.
Replaced other thread-crossing use of db_searcher, removed db_searcher from const_rethreading_metadata_accessor_t.
Removed unnecessarily cross-threaded const_rethreading_metadata_accessor_t::ns_searcher uses.
Removed comment about semilattice_metadata.
Merge branch 'next' into sam_1907
Merge branch 'sam_1907' into next
Made changefeeds send empty batches as necessary.
adding r.http jsonp result_format
Fixed a concurrency bug in changefeeds.
New parse_string cJSON code from upstream.
New parse_string cJSON code from upstream.

Conflicts:

	src/http/json/cJSON.cc
Fix for a regression in our cJSON variant.
Fix for a regression in our cJSON variant.
making r.http errors recoverable and include header/body data
Merge branch 'v1.12.x' into next
Merge branch 'next' of github.com:rethinkdb/rethinkdb into next
Merge branch 'masatoshi_2461' of github.com:Masatoshi/rethinkdb into Masatoshi-masatoshi_2461
Merge branch 'Masatoshi-masatoshi_2461' into next
fixing r.http tests