ENG-6478: Allow LIMIT PARTITION ROWS to be set, changed, and dropped

using ALTER TABLE
The current scripts expect a basic change block to start with a line containing " A VoltDB extension".(note the leading space, single space separators and it is case sensitive) 
By convention, this is usually the start of a // comment preceded by optional spaces and usually containing trailing detail like

        // A VoltDB extension to support LIMIT PARTITION ROWS

The end of the block is a line containing " End of VoltDB extension"
which is by convention a stand alone // comment preceded by optional spaces:

        // End of VoltDB extension
There are additional conventions used within these marked blocks for surrounding with structured block-comments any original HSQL code (on untouched lines) that we want to remove or replace.

Also, a few modules contain large-scale additions always at the bottom of the class file just before the final "}" -- these are marked according to a different convention, recognized by its use of an older version of the intro text and bars of asterisks. I suppose at some point, I'll globally replace this older convention for consistency.