pgsql: Wordsmithing of HS and SR documentation, with some wording

Log Message:
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Wordsmithing of HS and SR documentation, with some wording improvements
from Erik Rijkers too.

Modified Files:
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pgsql/doc/src/sgml:
high-availability.sgml (r1.44 -> r1.45)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/high-availability.sgml?r1=1.44&r2=1.45)