* The value of SXHASH on non-string/bitvector arrays should not
change when the contents of the array change (clhs sxhash,
clhs 18.1.2.2). So the commit in 0.9.15.21 is invalid.
* But luckily nothing requires us to use SXHASH for our own
tables. Change the definition of EQUAL-HASH to punt to EQ-HASH
for data types where EQUAL == EQL