loadf treats non-existent file and not-permitted file the same

[akaIDIOT]

As long as there's a default provided, a file that does not exist results in that default; that's by design. That same file existing but not permitted to be read is treated the exact same way, which may not be great. The caller might expect the file to be included (with load_name, primarily), where confidence ignoring that file is a bit of a surprise. Surprises are not good, here.

[akaIDIOT]

The standard lib does distinguish PermissionError from FileNotFoundError, both of which are currently caught by except OSError. See #131 for tiny diff, could that cause any other issues down the line, for confidence itself or users calling this? Would except OSError with a deprecation warning make sense?