Install the Rubinius bundle in isolation

Makes sure that installing Rubinius won't touch other gems outside the
build directory.

bin/ruby-build

@@ -444,7 +444,7 @@ build_package_ree_installer() {
 build_package_rbx() {
   local package_name="$1"
 
-  { bundle
+  { bundle --path=vendor/bundle
     ./configure --prefix="$PREFIX_PATH" $RUBY_CONFIGURE_OPTS
     rake install
     fix_rbx_gem_binstubs "$PREFIX_PATH"

test/build.bats

@@ -217,7 +217,7 @@ DEF
   stub rake false
   stub bundle \
     '--version : echo 1' \
-    ' : echo bundle >> build.log' \
+    ' : echo bundle "$@" >> build.log' \
     '--version : echo 1' \
     " exec rake install : { cat build.log; echo bundle \"\$@\"; } >> '$INSTALL_ROOT/build.log'"
 
@@ -229,7 +229,7 @@ DEF
   unstub bundle
 
   assert_build_log <<OUT
-bundle
+bundle --path=vendor/bundle
 rubinius-2.0.0: --prefix=$INSTALL_ROOT
 bundle exec rake install
 OUT