pgsql: Make documentation more direct about the handling of COPY files

Log Message:
-----------
Make documentation more direct about the handling of COPY files based on
the client encoding.

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
copy.sgml (r1.93 -> r1.94)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/copy.sgml?r1=1.93&r2=1.94)