Add top level build script for building packages.

ports/boost/build.sh

 #!/bin/bash
 # Copyright (c) 2011 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-source pkg_info
-source ../../build_tools/common.sh
 
 BUILD_ARGS="\
   --build-dir=${NACL_BUILD_SUBDIR} \
   --stagedir=${NACL_BUILD_SUBDIR} \
   link=static"
 
 # TODO(eugenis): build dynamic libraries, too
 if [ $NACL_GLIBC = "1" ] ; then
   BUILD_ARGS+=" --without-python --without-signals --without-mpi"
   BUILD_ARGS+=" --without-context --without-coroutine"
 else
   BUILD_ARGS+=" --with-date_time --with-program_options"
 fi
 
 ConfigureStep() {
   ChangeDir ${NACL_PACKAGES_REPOSITORY}/${PACKAGE_NAME}
   echo "using gcc : 4.4.3 : ${NACLCXX} ;" > tools/build/v2/user-config.jam
   LogExecute ./bootstrap.sh --prefix="${NACLPORTS_PREFIX}"
 }
 
 BuildStep() {
   Banner "Building ${PACKAGE_NAME}"
   LogExecute ./b2 stage ${BUILD_ARGS}
 }
 
 InstallStep() {
   Banner "Installing ${PACKAGE_NAME}"
   LogExecute ./b2 install ${BUILD_ARGS}
 }
-
-PackageInstall
-exit 0