Allow re-targeting of naclports install

libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh

Index: libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh
diff --git a/libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh b/libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh
index 74d2ea057eff4ddace6af27568a0194435f18407..43274b59bb20d82b42577d696957120cdcd9b01a 100755
--- a/libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh
+++ b/libraries/bzip2-1.0.6/nacl-bzip2-1.0.6.sh
@@ -28,12 +28,12 @@ CustomInstallStep() {
 
   # Don't rely on make install, as it implicitly builds executables
   # that need things not available in newlib.
-  mkdir -p ${NACL_SDK_USR}/include
-  cp -f bzlib.h ${NACL_SDK_USR}/include
-  chmod a+r ${NACL_SDK_USR}/include/bzlib.h
-  mkdir -p ${NACL_SDK_USR}/lib
-  cp -f libbz2.a ${NACL_SDK_USR}/lib
-  chmod a+r ${NACL_SDK_USR}/lib/libbz2.a
+  mkdir -p ${NACLPORTS_PREFIX}/include
+  cp -f bzlib.h ${NACLPORTS_PREFIX}/include
+  chmod a+r ${NACLPORTS_PREFIX}/include/bzlib.h
+  mkdir -p ${NACLPORTS_PREFIX}/lib
+  cp -f libbz2.a ${NACLPORTS_PREFIX}/lib
+  chmod a+r ${NACLPORTS_PREFIX}/lib/libbz2.a
 
   DefaultTouchStep
 }