Thread: pgsql: Add text to "Populating a Database" pointing out that bulk data

Log Message:
-----------
Add text to "Populating a Database" pointing out that bulk data load into a
table with foreign key constraints eats memory.  Per off-line discussion of
bug #5480 with its reporter.  Also do some minor wordsmithing elsewhere in
the same section.

Modified Files:
--------------
    pgsql/doc/src/sgml:
        perform.sgml (r1.79 -> r1.80)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/perform.sgml?r1=1.79&r2=1.80)