Added {ECLI_STRING_LONGVARCHAR}.make_force_maximum_capacity as creation routine

This fixes a bug where the query assistant generates a class with this
creation routine (when the length of a result column has been truncated
to `1000000' bytes).

Example:

        make
                        -- Creation of buffers
                do
                        ...
                        create col.make_force_maximum_capacity (1000000)
                        ...
                end