cleanups in cast API

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

.../src/com/oracle/truffle/r/nodes/builtin/base/Sample2.java

...tin/src/com/oracle/truffle/r/nodes/builtin/base/Scan.java

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

...c/com/oracle/truffle/r/nodes/builtin/base/Substitute.java

...c/com/oracle/truffle/r/nodes/builtin/CastBuilderTest.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

...c/com/oracle/truffle/r/nodes/binary/BoxPrimitiveNode.java

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

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

...com/oracle/truffle/r/nodes/builtin/casts/MessageData.java

...om/oracle/truffle/r/nodes/builtin/casts/PipelineStep.java

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

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

.../truffle/r/nodes/builtin/casts/fluent/ArgCastBuilder.java

...le/r/nodes/builtin/casts/fluent/FindFirstNodeBuilder.java

...truffle/r/nodes/builtin/casts/fluent/PipelineBuilder.java

.../r/nodes/builtin/casts/fluent/PreinitialPhaseBuilder.java