rename library download directory libdownloads, use lib for builtin shared libraries

.hgignore

com.oracle.truffle.r.native/builtinlibs/Makefile

com.oracle.truffle.r.native/fficall/jni/Makefile

com.oracle.truffle.r.native/gnur/Makefile.gnur

com.oracle.truffle.r.native/gnur/Makefile.libs

com.oracle.truffle.r.native/osextras/Makefile

.../truffle/r/parser/processor/GenerateRParserProcessor.java

...me.ffi/src/com/oracle/truffle/r/runtime/ffi/LibPaths.java

mx.fastr/mx_fastr.py

mx.fastr/suite.py