Import changes from install script of ruby-build v20131225.1

install.sh

@@ -1,17 +1,18 @@
 #!/bin/sh
+# Usage: PREFIX=/usr/local ./install.sh
+#
+# Installs pyenv-virtualenv under $PREFIX.
 
 set -e
 
+cd "$(dirname "$0")"
+
 if [ -z "${PREFIX}" ]; then
   PREFIX="/usr/local"
 fi
 
 BIN_PATH="${PREFIX}/bin"
 
-mkdir -p "${BIN_PATH}"
+mkdir -p "$BIN_PATH"
 
-for file in bin/*; do
-  cp "${file}" "${BIN_PATH}"
-done
-
-echo "Installed pyenv-virtualenv at ${PREFIX}"
+install -p bin/* "$BIN_PATH"