Log Message:
bvttest: Update to 20200610

changelog:
20200610
        + modify DECSCA test to show whether EL/ED and ECH/ICH/DCH ignore
          DECSCA.

        + modify DECERA test to assume that the terminal uses bce, and prompt
          for an additional color-change/erase to demonstrate this.

20200420
        + improve test-coverage for REP/SD/SL/SR/SU, exercising default params.

        + improve DA/DA2 reports for VT125, VT240, VT382, VT510 used in xterm.