org-table.el (org-table-copy-increment): Change increment behavior

org-table.el (org-table-copy-increment): Change increment behavior

* org-table.el (org-table-copy-increment): Use a number as a
way to force a fixed increment value.
(org-table-copy-down): Increment by the difference between the
current field and the field in the row above.  This is the
default behavior.  To go back to the previous behavior (to
always increment by 1 unit), set `org-table-copy-increment'
to 1.

Thanks to Michael Brand for suggesting this.