npgsql - Npgsql2: Fix resource manager lifetime.

Log Message:
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Fix resource manager lifetime. This improves System.Transaction support.

Modified Files:
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Npgsql2/src/Npgsql:
NpgsqlPromotableSinglePhaseNotification.cs (r1.7 -> r1.8)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/npgsql/Npgsql2/src/Npgsql/NpgsqlPromotableSinglePhaseNotification.cs.diff?r1=1.7&r2=1.8)