[PATCH 1/9] Adapt `info probes' to support printing probes of different types.

[Jose E. Marchesi]

Hi Sergio.
    
    > A "probe type" (backend for the probe abstraction implemented in probe.[ch])
    > can extend the information printed by `info probes' by defining additional
    > columns.  This means that when `info probes' is used to print all the probes
    > regardless of their types, some of the columns will be "not applicable" to
    > some of the probes (like, say, the Semaphore column only makes sense for
    > SystemTap probes).  This patch makes `info probes' fill these slots with "n/a"
    > marks (currently it breaks the table) and not include headers for which no
    > actual probe has been found in the list of defined probes.
    
    Thanks for the patch, Jose.  Comments below.

I agree/comply with all these comments :)