Merge remote-tracking branch 'remotes/mdroth/qga-pull-2014-02-24' into staging

* remotes/mdroth/qga-pull-2014-02-24:
  qemu-ga: isa-serial support on Windows
  qga: Fix memory allocation pasto
  qga: Don't require 'time' argument in guest-set-time command
  qga: vss-win32: Fix interference with snapshot deletion by other VSS request
  qga: vss-win32: Fix interference with snapshot creation by other VSS requesters
  qga: vss-win32: Use NULL as an invalid pointer for OpenEvent and CreateEvent

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>