npgsql - Npgsql2: Removed hardcoded path to nunit assemblies.

Log Message:
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Removed hardcoded path to nunit assemblies. Now use a dynamic property to get them. Thanks Gert Driesen (gert dot driesen -at- ardatis dot com) from nant dev team for coding this property. Now, Npgsql tests are easier to run.

Modified Files:
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Npgsql2/testsuite/noninteractive/NUnit20:
NpgsqlTests.build (r1.1 -> r1.2)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/npgsql/Npgsql2/testsuite/noninteractive/NUnit20/NpgsqlTests.build.diff?r1=1.1&r2=1.2)