pgsql: Improve description of --disable-rpath workaround for regression

Log Message:
-----------
Improve description of --disable-rpath workaround for regression test
problems.

Modified Files:
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pgsql/doc/src/sgml:
regress.sgml (r1.43 -> r1.44)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/regress.sgml.diff?r1=1.43&r2=1.44)