Edited Issue: Some unit tests fails if all the test suite is run [39]

Same behavior run on Windows 7, 64 bits, run from VS2013 test explorer.

If run individually, 6 of the tests pass. If all test run, they fail and subsequently fail even if run alone.

Recent work on https://rdotnet.codeplex.com/workitem/77 provides new insight however: likely that the default packages could not be loaded by the R engine. May have a big payoff if this issue is better understood.

Test Name: TestGC
Test FullName: RDotNet.REngineTest.TestGC
Test Outcome: Failed
Test Duration: 0:00:00.002

Result Message: RDotNet.EvaluationException : Error: could not find function "memory.size"
Result StackTrace:
at RDotNet.REngine.Parse(String statement, StringBuilder incompleteStatement) in f:\codeplex\rdotnet\R.NET\REngine.cs:line 545
at RDotNet.REngine.<Defer>d__0.MoveNext() in f:\codeplex\rdotnet\R.NET\REngine.cs:line 458
at System.Linq.Enumerable.LastOrDefault[TSource](IEnumerable`1 source)
at RDotNet.REngine.Evaluate(String statement) in f:\codeplex\rdotnet\R.NET\REngine.cs:line 423
at RDotNet.REngineTest.TestGC() in f:\codeplex\rdotnet\RDotNet.Tests\REngineTest.cs:line 49

Test Name: TestGenericFunction
Test FullName: RDotNet.RFunctionsTest.TestGenericFunction
Result Message: RDotNet.EvaluationException : Error: could not find function "setGeneric"

Test Name: TestGetRow
Test FullName: RDotNet.DataFrameRowMappingTest.TestGetRow

Result Message: RDotNet.EvaluationException : Error: object 'iris' not found