[emirmrkaljevic]

Fixes #15922

fmt now reports a file operand it can't open or that is a directory, sets exit status 1, and continues with the remaining files, like GNU. The directory case prints error reading 'dir': Is a directory (GNU's wording) instead of a bare read error; the unused ReadError variant and its fmt-error-read string are replaced by fmt-error-reading-is-directory (en-US and fr-FR).

Found with behave, comparing against GNU coreutils 9.12: fmt d a.txt, fmt missing a.txt, fmt a.txt d, fmt d and fmt d missing now give the same stdout, stderr and exit code as GNU.

Tests: test_fmt_directory, test_fmt_continues_after_directory (both skipped on Windows, where a directory can't be opened as a file) and test_fmt_continues_after_missing_file.

[cakebaker]

Thanks!