pgsql: In the release checklist, mention packagers will see the minor

Log Message:
-----------
In the release checklist, mention packagers will see the minor upgrade
numbering for additional functions.

Modified Files:
--------------
pgsql/src/tools:
RELEASE_CHANGES (r1.78 -> r1.79)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/RELEASE_CHANGES?r1=1.78&r2=1.79)