Added failing test while importing stylesheets with erb handlers
Exhibits Sass::SyntaxError "File to import not found or unreadable"
while trying to import a stylesheet of the form file.{css,scss}.erb

[#139]
Add support for importing (.css,.scss,.sass).erb files. Fixes #139 #153.
dont override private sass api
Merge pull request #154 from rails/erb_support

Add ERB support