Update to xenstore 1.2.4 (watching bug)

Signed-off-by: David Scott <dave.scott@eu.citrix.com>
Merge pull request #192 from djs55/fix-watching-bug

Update to xenstore 1.2.4 (watching bug)
sm: Move drivers to /usr/lib/xapi/sm

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #193 from euanh/build-improvements

sm: Move drivers to /usr/lib/xapi/sm