`dolt_status` table unhelpful during merge when there are constraint violations.

[timsehn]

Repro:

1. Clone https://www.dolthub.com/repositories/timsehn/three_way_merge
2. In a sql server, merge fire-tim into main

   
   three_way_merge/main> call dolt_merge('fire-tim');
   +------+--------------+-----------+-----------------+
   | hash | fast_forward | conflicts | message         |
   +------+--------------+-----------+-----------------+
   |      | 0            | 1         | conflicts found |
   +------+--------------+-----------+-----------------+
   1 row in set (0.00 sec)

three_way_merge/main> select * from dolt_status; +------------+--------+----------+ | table_name | staged | status | +------------+--------+----------+ | employees | 0 | modified | +------------+--------+----------+ 1 row in set (0.00 sec)

This should say `constraint violation` in status instead of modified. In the case of a schema conflict it says:

three_way_merge/main> select * from dolt_status; +------------+--------+-----------------+ | table_name | staged | status | +------------+--------+-----------------+ | employees | 0 | schema conflict | +------------+--------+-----------------+