npgsql - Npgsql2: Added support to parse "-infinity" and "infinity"

Log Message:
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Added support to parse "-infinity" and "infinity" date values.

Modified Files:
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Npgsql2/src/NpgsqlTypes:
DateDatatypes.cs (r1.10 -> r1.11)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/npgsql/Npgsql2/src/NpgsqlTypes/DateDatatypes.cs?r1=1.10&r2=1.11)