support WEEK as a selector of EXTRACT, and refactor test cases for EXTRA...

...CT
There is a standard extension to our structured comments for use when changing (not just adding) original HSQL code. It is intended to leave the original HSQL line unchanged but disabled.
In this case, it would look something like this (except it wants to preserve the exact spacing of the disabled HSQL line).

        // A VoltDB extension to use FLOAT as the official DOUBLE type name
        public static final int WEEK = 617;
        /* disable 1 line ...
        static final int WEEK = 617;
        ... disabled 1 line */
        // End of VoltDB extension