Added more informative exception when using helper :some_helper and the helper requires another file that fails, you'll get an error message tells you what file actually failed to load, rather than falling back on assuming it was the helper file itself #346 [dblack]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@250 5ecf4fe2-1ee6-0310-87b1-e25e094e27de