* (44) spec bug: GrB_Matrix_diag was implemented in v5.2.x and v6.x with
the wrong signature. This fix requires the major release to change,
from v6.x to v7.x, since the change means that the revised v7 is not
backward compatible with v6.
* performance for GrB_mxm: auto selection for saxpy method (Hash vs
Gustavson) revised.
* (43) performance bug fix for GrB_assign: better performance for
C(i,j)=scalar and C(i,j)+=scalar when i and j have length 1 (scalar
assigment with no scalar expansion). The prior code worked but this is
a performance bug introduced in the parallel GraphBLAS. The bug likely
doesn't appear in v2.x (the sequential version of SS:GrB). This
affects method 1 of Demo/Source/wathen.c. Caught by a reviewer of the
ACM TOMS paper on the parallel GraphBLAS.