Allow re-targeting of naclports install

libraries/dreadthread/nacl-dreadthread.sh

Index: libraries/dreadthread/nacl-dreadthread.sh
diff --git a/libraries/dreadthread/nacl-dreadthread.sh b/libraries/dreadthread/nacl-dreadthread.sh
index a35232d9edf480bdeda6b141aa11bc35d474cb48..858af11d57af3a9228b007ac633971984d3bd295 100755
--- a/libraries/dreadthread/nacl-dreadthread.sh
+++ b/libraries/dreadthread/nacl-dreadthread.sh
@@ -32,10 +32,10 @@ CustomBuildStep() {
 CustomInstallStep() {
   Banner "Installing ${PACKAGE_NAME}"
   export PACKAGE_DIR="${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}"
-  cp ${PACKAGE_DIR}/libdreadthread.a ${NACL_SDK_USR_LIB}
-  cp ${START_DIR}/dreadthread.h ${NACL_SDK_USR_INCLUDE}
-  cp ${START_DIR}/dreadthread_ctxt.h ${NACL_SDK_USR_INCLUDE}
-  cp ${START_DIR}/dreadthread_chain.h ${NACL_SDK_USR_INCLUDE}
+  cp ${PACKAGE_DIR}/libdreadthread.a ${NACLPORTS_LIBDIR}
+  cp ${START_DIR}/dreadthread.h ${NACLPORTS_INCLUDE}
+  cp ${START_DIR}/dreadthread_ctxt.h ${NACLPORTS_INCLUDE}
+  cp ${START_DIR}/dreadthread_chain.h ${NACLPORTS_INCLUDE}
   DefaultTouchStep
 }