Introduce v3 of savevm protocol

Introduce v3 of savevm protocol

The current savevm/loadvm protocol has some draw backs.  It does not support
the ability to do progressive saving which means it cannot be used for live
checkpointing or migration.  The sections sizes are 32-bit integers which
means that it will not function when using more than 4GB of memory for a guest.
It attempts to seek within the output file which means it cannot be streamed.
The current protocol also is pretty lax about how it supports forward
compatibility.  If a saved section version is greater than what the restore
code support, the restore code generally treats the saved data as being in
whatever version it supports.  This means that restoring a saved VM on an older
version of QEMU will likely result in silent guest failure.

This patch introduces a new version of the savevm protocol.  It has the
following features:

 * Support for progressive save of sections (for live checkpoint/migration)
 * An asynchronous API for doing save
 * Support for interleaving multiple progressive save sections
   (for future support of memory hot-add/storage migration)
 * Fully streaming format
 * Strong section version checking

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5434 c046a42c-6fe2-441c-8c8c-71466251a162