pgsql: Update TODO: o Allow COPY in CSV mode to control whether

Log Message:
-----------
Update TODO:

o Allow COPY in CSV mode to control whether a quoted zero-length
string is treated as NULL

Currently this is always treated as a zero-length string,
which generates an error when loading into an integer column

Modified Files:
--------------
pgsql/doc:
TODO (r1.2310 -> r1.2311)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/TODO?r1=1.2310&r2=1.2311)
pgsql/doc/src/FAQ:
TODO.html (r1.819 -> r1.820)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/FAQ/TODO.html?r1=1.819&r2=1.820)