yet more RFFI refactoring; set RFFI tempDir correctly

com.oracle.truffle.r.native/fficall/jni/src/rfficall.c

com.oracle.truffle.r.native/fficall/jni/src/rffiutils.h

com.oracle.truffle.r.native/fficall/jni/src/variables.c

...e.ffi/src/com/oracle/truffle/r/runtime/ffi/RFFIUtils.java

...i/src/com/oracle/truffle/r/runtime/ffi/RFFIVariables.java

...rc/com/oracle/truffle/r/runtime/ffi/jnr/JNI_CallRFFI.java

...fi/src/com/oracle/truffle/r/runtime/ffi/jnr/JNR_Base.java

.../src/com/oracle/truffle/r/runtime/ffi/jnr/JNR_Lapack.java

...i/src/com/oracle/truffle/r/runtime/ffi/jnr/JNR_RAppl.java

...i/src/com/oracle/truffle/r/runtime/ffi/jnr/JNR_Stats.java

...untime/src/com/oracle/truffle/r/runtime/TempPathName.java

...untime/src/com/oracle/truffle/r/runtime/ffi/CallRFFI.java