com_setatt(): Allow to specify a file name pattern.

The help text of the setatt command claims that file name patterns
may be specified as arguments. The text also contains an example which
involves a wildcard pattern. However, this never worked as advertised
since the command actually accepts only full paths.

This commit teaches the command to process the given arguments as
patterns by employing the same pattern matching loop that is also
used by other commands.

In addition we now also send a "no matches" message to the client
in case there was no match. Previously the command stayed silent and
terminated successfully in this case.