URL encoded inputs for file uris not correctly parsed

An input file contains URIs that have been urlencoded. This results in errors such as:

The specified file private://example%28v3%29%281%29.pdf could not be copied, because no file by that name exists. Please check that you supplied the correct filename.

It could be possible to fix this with a feeds_tamper_php plugin to do urldecode() but I am not sure if this is intended behaviour and have included a patch to file.inc that works for me.