Non existant partial inclusions fail silently

[Kissaki]

When including partial files for parsing ({{> filename }}) from Mustache.render_from_file and the file is not found, no issue or error is returned. Instead, the the lib returns a parsed template as if nothing went wrong.

I would expect and error to be raised/nothing to be returned to indicate an error.

[jverzani]

This is due to something I added where {{> name }} is looked up first as a file name, and then as a value within the context. I can add an error if that latter doesn't resolve.

[jverzani]

Actually, in testing to try and fix #82, I see this test: "The empty string should be used when the named partial is not found", so the current behavior seems to be the expected behavior.