call vendored virtualenv script

bin/compile

@@ -4,6 +4,7 @@
 set -eo pipefail
 
 BIN_DIR=$(cd $(dirname $0); pwd) # absolute path
+ROOT_DIR=$(dirname $BIN_DIR)
 BUILD_DIR=$1
 CACHE_DIR=$2
 
@@ -11,6 +12,11 @@ NAME=$($BIN_DIR/detect $BUILD_DIR)
 PIP_DOWNLOAD_CACHE=${PIP_DOWNLOAD_CACHE:-$CACHE_DIR/pip_downloads}
 VIRTUALENV_DIRS="bin include lib"
 
+virtualenv() {
+  VENV_PATH=$ROOT_DIR/src/virtualenv-1.6.4
+  PYTHONPATH=$VENV_PATH python $VENV_PATH/scripts/virtualenv "$@"
+}
+
 indent() {
   RE="s/^/       /"
   [ $(uname) == "Darwin" ] && sed -l "$RE" || sed -u "$RE"