bug#9594: 27.3 Numeric modes (File permissions): Special mode bits assume file is regular

[Filipus Klutiero]

Section 27.3 Numeric modes contains:

> Here is how the bits are arranged, starting with
> the lowest valued bit:
>
>      Value in  Corresponding
>      Mode      Mode Bit
>
>                Other users not in the file's group:
>         1      Execute/search
>         2      Write
>         4      Read
>
>                Other users in the file's group:
>        10      Execute/search
>        20      Write
>        40      Read
>
>                The file's owner:
>       100      Execute/search
>       200      Write
>       400      Read
>
>                Special mode bits:
>      1000      Restricted deletion flag or sticky bit
>      2000      Set group ID on execution
>      4000      Set user ID on execution

These correspondences assume that the file is a regular file. For 
example, for a directory (where execution doesn't make sense), 2000 
causes files created in the directory to inherit the directory's group. 
http://en.wikipedia.org/wiki/Setgid#setuid_and_setgid_on_directories has 
more information.