Add a SEARCH_NOCONTENT method

[guyroyse]

Sometimes you just want the number and names of the keys that match a search but don't want the values in the Hashes or JSON documents themselves. Right now, you need to pass in an empty array for RETURN in the search options. This is fiddly and inconvenient and, more importantly, doesn't work. See #2364.

Regardless, a SEARCH_NOCONTENT method would make this easier and more intuitive for users. And more likely to be used.