Allow re-targeting of naclports install

libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh

Index: libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
diff --git a/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh b/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
index 01e39a21aa3416c9b0e053b050e1991d9f29978e..3183cab8fefca1341677fb9d55e7e03333bcbbd3 100755
--- a/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
+++ b/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
@@ -15,8 +15,8 @@ source ../../build_tools/common.sh
 
 
 CustomConfigureStep() {
-  export PKG_CONFIG_PATH=${NACL_SDK_USR_LIB}/pkgconfig
-  export PKG_CONFIG_LIBDIR=${NACL_SDK_USR_LIB}
+  export PKG_CONFIG_PATH=${NACLPORTS_LIBDIR}/pkgconfig
+  export PKG_CONFIG_LIBDIR=${NACLPORTS_LIBDIR}
   export PATH=${NACL_BIN_PATH}:${PATH};
   MakeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}/${PACKAGE_NAME}-build
   ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}/${PACKAGE_NAME}-build
@@ -48,8 +48,8 @@ CustomConfigureStep() {
     --disable-ffserver \
     --disable-demuxer=rtsp \
     --disable-demuxer=image2 \
-    --prefix=${NACL_SDK_USR} \
-    --libdir=${NACL_SDK_USR_LIB}
+    --prefix=${NACLPORTS_PREFIX} \
+    --libdir=${NACLPORTS_LIBDIR}
 }