pgsql-server: Add explicit note that empty-string array element values

Log Message:
-----------
Add explicit note that empty-string array element values now have to
be written with quotes. Minor copy-editing too.

Modified Files:
--------------
pgsql-server/doc/src/sgml:
release.sgml (r1.292 -> r1.293)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/doc/src/sgml/release.sgml.diff?r1=1.292&r2=1.293)