The primary purpose of this patch is to add support for non-polling 
access to the xen trace buffers. The hypervisor changes have already 
been accepted.

Also included are a few bug fixes and some minor new features:

1. If xenmon is run without first allocating trace buffers (via 
'setsize') and enabling them (via 'tbctl'), then this is done 
automatically using sensible defaults.

2. There was a bug that caused the first second's worth of data output 
from xenmon to be erroneous; This has been fixed.

3. There was a bug that caused xenmon to sometimes not display data for 
newly created domains; This has also been fixed.

4. The xenmon display has a 'heartbeat' which flickers once per second. 
This is to show that xenmon is still alive, even though the display 
isn't changing at all, a situation that can happen sometimes when there 
is nothing at all happening on a particular cpu.

5. Added cpu utilization display to the top of the xenmon window.

6. Added a bunch of options in xenmon to control exactly which metrics 
are displayed, so the screen doesn't get cluttered with stuff you're not 
interested in. The new options are:
  --allocated
  --noallocated
  --blocked
  --noblocked
  --waited
  --nowaited
  --excount
  --noexcount
  --iocount
  --noiocount

7. Added an option ("--cpu=N") to xenmon to specify which physical cpu 
you'd like data displayed for.

8. Updated the README with information about default trace buffer size, etc.

Signed-off-by: Rob Gardner <rob.gardner@hp.com>