Basic version of get_full_megeath_table works!

Except that I forgot the J, H, K columns!
Fixed get_full_megeath_table by adding in the JHK columns!
Added the 'truncated' option to get_full_megeath_table.

It trims the table spatially, so that only our field is included.
(this greatly speeds up the source cross-matching; the returned table is reduced in size from 306,162 rows to 13,672 rows!)