various performance fixes

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

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

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

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

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

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

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

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

...rc/com/oracle/truffle/r/nodes/builtin/base/Transpose.java

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

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

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

...m/oracle/truffle/r/nodes/builtin/base/WhichFunctions.java