Updates to make MySQL and sqlite work

Neither MySQL nor sqlite support the SQL 2008 standard FETCH clause, which we use as 'fetch next (n) rows only'.  As such, I had to extend their dialects to supply their LIMIT clause.  Note that this is *not* perfect - this code assumes that any non-standard LIMIT clause must come *before* the OFFSET clause (which it does in MySQL, at least).  However, the OFFSET clause *must* come before the FETCH clause in standard SQL.  This makes for some ugly code - I'll revisit it and probably combine offset and limit into a single method call on these dialects, later.

Note that during initialization of a query, the constructor will automatically convert MySQL and sqlite dialects from gorp to our extended dialects.