As a lead-in to some upcoming work on "OS awareness" for Linux GDB, here 
is a little patch for "info os" to return the types of data available 
(which is currently just "processes"), instead of erroring out.

Stan

2010-06-14  Stan Shebs  <stan@codesourcery.com>

    * osdata.c (get_osdata): Warn separately if target does not report
    type list.
    (info_osdata_command): Allow empty type, report error if target
    does not return available types of OS data.
    * linux-nat.c (linux_nat_xfer_osdata): Report list of OS data
    types if no annex supplied.