fix various warnings, unused imports, etc.

...ine/src/com/oracle/truffle/r/engine/TruffleRLanguage.java

...om/oracle/truffle/r/library/methods/SubstituteDirect.java

...c/com/oracle/truffle/r/library/stats/SplineFunctions.java

...cle/truffle/r/nodes/builtin/base/ConnectionFunctions.java

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

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

...racle/truffle/r/nodes/binary/BinaryArithmeticSpecial.java

...m/oracle/truffle/r/nodes/binary/BinaryBooleanSpecial.java

.../src/com/oracle/truffle/r/nodes/ffi/CoerceVectorNode.java

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

...rc/com/oracle/truffle/r/runtime/conn/FileConnections.java

...src/com/oracle/truffle/r/runtime/conn/RawConnections.java