[GR-2798] Fixes for testthat.

...oracle/truffle/r/library/methods/MethodsListDispatch.java

....r.library/src/com/oracle/truffle/r/library/stats/model.R

.../src/com/oracle/truffle/r/nodes/builtin/base/Combine.java

...acle/truffle/r/nodes/builtin/base/ConditionFunctions.java

.../com/oracle/truffle/r/nodes/builtin/base/ListBuiltin.java

...in/src/com/oracle/truffle/r/nodes/builtin/base/Order.java

...n/src/com/oracle/truffle/r/nodes/builtin/base/Repeat.java

...test/src/com/oracle/truffle/r/nodes/casts/MarkLookup.java

...com/oracle/truffle/r/nodes/casts/ResultTypesAnalyser.java

...rc/com/oracle/truffle/r/nodes/casts/SamplesCollector.java

...s/src/com/oracle/truffle/r/nodes/builtin/CastBuilder.java

.../src/com/oracle/truffle/r/nodes/builtin/casts/Filter.java

...cle/truffle/r/nodes/builtin/casts/PipelineToCastNode.java

...nodes/builtin/casts/analysis/ForwardedValuesAnalyser.java

...fle/r/nodes/builtin/casts/fluent/InitialPhaseBuilder.java

....nodes/src/com/oracle/truffle/r/nodes/unary/CastNode.java

.../com/oracle/truffle/r/nodes/unary/RVarArgsFilterNode.java

.../src/com/oracle/truffle/r/runtime/ArgumentsSignature.java

....r.runtime/src/com/oracle/truffle/r/runtime/RDeparse.java

...me/src/com/oracle/truffle/r/runtime/context/RContext.java