reimplement db:reindex_search using tire api; avoid OOM errors
Merge branch 'master' into feature/jsa/ds-reindex

Conflicts:
	Rakefile
reindex_search: refactoring and improvements
* properly handle when the index/alias don't yet exist
* don't lose content updates made while reindex/rebuild are in progress
* when possible, use tire api's reindex call for much more efficient index changes
* expose rake tasks to explicitly rebuild or reindex individual types
quick fix to skip the second document reimport when it is *not* necessary (first time index creation).
Merge pull request #49 from edx/feature/jsa/ds-reindex

restore deep search with reindex fix