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 e1e30bc013c2fcf57366d21c5115ee1424de5b2e..2033dd29603a498244988d96ab6c6941316d15d2 100755
--- a/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
+++ b/libraries/ffmpeg-0.5/nacl-ffmpeg-0.5.sh
@@ -19,8 +19,8 @@ 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}/${PACKAGE_NAME}-build
@@ -52,8 +52,8 @@ CustomConfigureStep() {
     --disable-ffserver \
     --disable-demuxer=rtsp \
     --disable-demuxer=image2 \
-    --prefix=${NACL_SDK_USR} \
-    --libdir=${NACL_SDK_USR_LIB}
+    --prefix=${NACLPORTS_PREFIX} \
+    --libdir=${NACLPORTS_LIBDIR}
 }