cat: exit(1) for bad arguments

[mknos]

• Previously on my system directory arguments would silently be ignored instead of flagging an error
• Make $options more pretty
• Declare $Program and exit code constants as done in other scripts
• Explicitly check for directory before open() as done in other scripts
• Error exit if one or more files cannot be opened, or is a directory
• Lone '-' argument is still handled for stdin
• The <> loop over all input files becomes explicit do_file() call per argument
• case1: perl cat F1 . will print F1, warn about directory '.' then exit(1)
• case2: perl cat F1 F2 will warn about F1 not existing, proceed to print F2 then exit(1)

[briandfoy]

Very nice. Thanks,