Make the event-channel pending and mask arrays consist of

Make the event-channel pending and mask arrays consist of
longs. Thi sensures appropriate alignment for architectures
that require it, and also allows us to naturally support up
to 4096 event channels per 64-bit guest.

Moved 'n_vcpu' field from shared_info to start_info. Really it
ought to disappear altogether as the info can be derived from
xenstore.

Fix a weird bug in XendDomainInfo where 'vcpus' information for
a domain defaults to floating point value 1.0 rather than integer
1. This looks like a Python bug to me, but in any case it is
'fixed' by explicitly converting the default value to an integer.

Signed-off-by: Keir Fraser <keir@xensource.com>