Right now, snapshot_conf.h is rather large - it deals with three
separate types: virDomainSnapshotDef (the snapshot definition as it
maps to XML), virDomainSnapshotObj (an object containing a def and the
relationship to other snapshots), and virDomainSnapshotObjList (a list
of snapshot objects), where two of the three types are currently
public rather than opaque.  What's more, the types are circular: a
snapshot def includes a virDomainPtr, which contains a snapshot list,
which includes a snapshot object, which includes a snapshot def.

In order to split the three objects into separate files, while still
allowing each header to use sane typedefs to incomplete pointers, the
obvious solution is to lift the typedefs into yet another header, with
no other dependencies.  Start the split by factoring out all struct
typedefs from domain_conf.h (enum typedefs don't get used in function
signatures, and function typedefs tend not to suffer from circular
referencing, so those stay put).  The only other exception is
virDomainStateReason, which is only ever used directly rather than via
a pointer.

This patch is just straight code motion (all typedefs are listed in
the same order before and after the patch); a later patch will sort
things for legibility.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>