The attached patch: * Arranges for the sonames of libxenstore, libxc and libblktap to be set from a single place in Config.mk. * Bumps the soname major version number to 3.2 in preparation for 3.2 rc1 after which we do not expect to have ABI changes.

I have not done anything about libaio, libfsimage and libflask. The former two are from important elsewhere and if we're lucky will have sane versioning upstream.

libflask has a very small interface and I'm hoping that the XSM authors have been keeping some ABI discipline.