Clarify the choice of rscale in numeric_sqrt().
Improve the comment explaining the choice of rscale in numeric_sqrt(),
and ensure that the code works consistently when other values of
NBASE/DEC_DIGITS are used.
Note that, in practice, we always expect DEC_DIGITS == 4, and this
does not change the computation in that case.
Joel Jacobson and Dean Rasheed
Discussion: https://postgr.es/m/
06712c29-98e9-43b3-98da-
f234d81c6e49%40app.fastmail.com