Properly handle file:// URIs when trying to cache local files
Properly handle file:// URIs when trying to cache local files

This fixes a regression introduced between 2014.1.0 and now, likely
around the time when we moved to using the requests library. It allows
for local file paths (either prefixed with 'salt://' or not) to be
"cached" by simply returning the file path.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt