Allow re-targeting of naclports install

libraries/libtommath-0.41/nacl-libtommath-0.41.sh

Index: libraries/libtommath-0.41/nacl-libtommath-0.41.sh
diff --git a/libraries/libtommath-0.41/nacl-libtommath-0.41.sh b/libraries/libtommath-0.41/nacl-libtommath-0.41.sh
index ec9f2aadb3cd429a92c579417a3cd583f0640528..f4d05b46c94dd67d1360133313ff7c4a9272d701 100755
--- a/libraries/libtommath-0.41/nacl-libtommath-0.41.sh
+++ b/libraries/libtommath-0.41/nacl-libtommath-0.41.sh
@@ -39,13 +39,13 @@ CustomBuildStep() {
 
 CustomInstallStep() {
   # copy libs and headers manually
-  Banner "Installing ${PACKAGE_NAME} to ${NACL_SDK_USR}"
-  ChangeDir ${NACL_SDK_USR_INCLUDE}
+  Banner "Installing ${PACKAGE_NAME} to ${NACLPORTS_PREFIX}"
+  ChangeDir ${NACLPORTS_INCLUDE}
   Remove ${PACKAGE_NAME}
   MakeDir ${PACKAGE_NAME}
   readonly THIS_PACKAGE_PATH=${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
   cp ${THIS_PACKAGE_PATH}/*.h ${PACKAGE_NAME}/
-  ChangeDir ${NACL_SDK_USR_LIB}
+  ChangeDir ${NACLPORTS_LIBDIR}
   cp ${THIS_PACKAGE_PATH}/*.a .
   DefaultTouchStep
 }