pgsql: Further improve documentation of the role-dropping process.

Further improve documentation of the role-dropping process.

In commit 1ea0c73c2 I added a section to user-manag.sgml about how to drop
roles that own objects; but as pointed out by Stephen Frost, I neglected
that shared objects (databases or tablespaces) may need special treatment.
Fix that.  Back-patch to supported versions, like the previous patch.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/f9fc8e79cd44a755a397886e791eefffacf02a2a

Modified Files
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doc/src/sgml/user-manag.sgml |   25 ++++++++++++++++++-------
1 file changed, 18 insertions(+), 7 deletions(-)