Allow stdin and directly named files to be excluded from check

For the sake of IDEs, check filename for exclusion even if the file is directly
named in the command line.

Also, if the filename is "-" (stdin) check the provided display name for
exclusion.

Also, avoid calling path checking functions on the "-" filename:

 * fnmatch.fnmatch()
 * os.path.isdir()
 * os.path.exists()