[RFC 0/5] Implenent 'frame apply COMMAND', enhance 'thread apply COMMAND'

[Philippe Waroquiers <philippe dot waroquiers at skynet dot be>]

This patch series :
 * implements a new command
     'frame apply [all | COUNT | -COUNT] [-FLAGS...] COMMAND'.
 * enhance 'thread apply COMMAND' by adding a -FLAGS argument
 * adds some shortcuts commands
 * documents the above in gdb.texinfo and NEWS.

Th new command 'frame apply' allows to apply a COMMAND to a number of frames,
or to all frames.
The optional -FLAGS... argument allows to control what output to produce
and how to handle errors raised when applying COMMAND to a frame.

Some examples usages for this new command:
   frame apply all info frame
      Produce info frame for all frames
   frame apply all p $sp
      For each frame, print the location, followed by the frame sp
   frame apply all -qq p $sp
      Same as before, but -qq flags (q = quiet) indicate to only print
      the frames sp.
   frame apply all -vv p $sp
      Same as before, but -vv flags (v = verbose) indicate to print
      location and source line for each frame.
   frame apply all p some_local_var_somewhere
      Print some_local_var_somewhere in all frames. 'frame apply'
      will abort as soon as the print command fails.
   frame apply all -c p some_local_var_somewhere
      Same as before, but -c flag (c = continue) means to
      print the error and continue applying command in case the
      print command fails.
   frame apply all -s p some_local_var_somewhere
      Same as before, but -s flag (s = silent) means to
      be silent for frames where the print command fails.
      In other words, this allows to 'search' the frame in which
      some_local_var_somewhere can be printed.

'thread apply' command has been enhanced to also accepts a -FLAGS...
argument.

Some examples usages for this new argument:
   thread apply all -s frame apply all -s p some_local_var_somewhere
      Prints the thread id, frame location and some_local_var_somewhere
      value in frames of threads that have such local var.

To make the life of the user easier, the most typical use cases
have shortcuts :
   faas  : shortcut for 'frame apply all -s'
   taas  : shortcut for 'thread apply all -s'
   tfaas : shortcut for 'thread apply all -s frame apply all -s"

An example usage :
   tfaas p some_local_var_somewhere
     same as the longer:
        'thread apply all -s frame apply all -s p some_local_var_somewhere'

The patch serie provides the implementation and all user visible documentation.

What is still missing is:
   * Missing regression tests.
     Not yet done as this is painful, and so is better done once there is
     an agreement on the behaviour.

   * Missing ChangeLog.
     Not yet done as this is painful, and is IMO close to or completely useless.
     So, I will do it for the (first) RFA, once the flow of RFC comments
     stops :).