adding a :query prefix option

This feature adds the ability to evaluate if a prefix should be added on a per term basis when the user specifies * in the query term.  Useful when searching for company names which do not stem naturally and when we only want to prefix one of the term instead of every term.

Specifying :prefix => :query in the pg search option will turn on this feature.

For instance, if I have a customer name of "Directbuy of Cincinatti" it can be found using "Directbuy Cin*"  and target the prefix search.