Replace

Compiles an replace into string and runs the query.
Because PostgreSQL doesn't support the replace into command,
we simply do a DELETE and an INSERT on the first key/value
combo, assuming that it's either the primary key or a unique key.

@param array   $set       An associative array of insert values
@param boolean $returnSQL

@return   mixed
@throws   DatabaseException
@internal param true $bool returns the generated SQL, false executes the query.