Fix rounding problem in dynahash.c's decision about when the target

Fix rounding problem in dynahash.c's decision about when the target
fill factor has been exceeded.  We usually run with ffactor == 1, but
the way the test was coded, it wouldn't split a bucket until the actual
fill factor reached 2.0, because of use of integer division.  Change
from > to >= so that it will split more aggressively when the table
starts to get full.