Unfortunately I have no time to work on this myself, but in order to
make progress I recommend checking in things piecemeal so that the same
changes don't get reviewed over and over again.  I propose that each
submit reference this bug ("Partial fix for issue #1621" I'd suggest)
and that the submits are recorded here (e.g. "fixed <filename> in rXXX
(2.5.2), rYYY (2.6)").  Then hopefully only a few hard cases will remain.

With Neal, I don't see what the warning in _csv is about. What condition
is being turned into a constant? Is the compiler perhaps rearranging the
code so as to insert "if (field[0] == '\0') goto XXX;" in front of the
for-loop where XXX jumps into the middle of the condition in the
if-statement immediately following the for-loop, and skipping that
if-block when breaking of the loop later? That would be clever, and
correct, and I'm not sure if making i unsigned is going to help -- in
fact it might make the compiler decide it can't use that optimization...