Branch Xen 4.9: Make staging be an unstable branch

Branch Xen 4.9: Make staging be an unstable branch

Config.mk
  MINIOS_UPSTREAM_REVISION   } changed from tag to equivalent
  QEMU_TRADITIONAL_REVISION  }  specific commit hash
  QEMU_UPSTREAM_REVISION     now tracking master again

README, xen/Makefile
  Update version number

*/configure
  Reran autoconf; only change is version number

tools/Rules.mk, xen/Kconfig.debug
  Enable debug.
  Reverts 229ff3125b3d "Use non-debug build for Xen 4.9".

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>