Enabled knitr

...ruffle/r/library/fastrGrid/grDevices/R/fastrGridDevices.R

...om/oracle/truffle/r/nodes/builtin/base/GrepFunctions.java

...truffle/r/nodes/builtin/base/HiddenInternalFunctions.java

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

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

...e.r.runtime/src/com/oracle/truffle/r/runtime/RSource.java

...e.r.runtime/src/com/oracle/truffle/r/runtime/RSrcref.java

com.oracle.truffle.r.test.packages/r/install.packages.R

.../com/oracle/truffle/r/test/builtins/TestBuiltin_gsub.java

...com/oracle/truffle/r/test/builtins/TestBuiltin_nchar.java