Extend the 'gendispatch.pl' script to be able to generate
three new types of file.

- 'aclheader' - defines signatures of helper APIs for
  doing authorization checks. There is one helper API
  for each API requiring an auth check. Any @acl
  annotations result in a method being generated with
  a suffix of 'EnsureACL'. If the ACL check requires
  examination of flags, an extra 'flags' param will be
  present. Some examples

  extern int virConnectBaselineCPUEnsureACL(void);
  extern int virConnectDomainEventDeregisterEnsureACL(virDomainDefPtr domain);
  extern int virDomainAttachDeviceFlagsEnsureACL(virDomainDefPtr domain, unsigned int flags);

  Any @aclfilter annotations resuilt in a method being
  generated with a suffix of 'CheckACL'.

  extern int virConnectListAllDomainsCheckACL(virDomainDefPtr domain);

  These are used for filtering individual objects from APIs
  which return a list of objects

- 'aclbody' - defines the actual implementation of the
  methods described above. This calls into the access
  manager APIs. A complex example:

    /* Returns: -1 on error (denied==error), 0 on allowed */
    int virDomainAttachDeviceFlagsEnsureACL(virConnectPtr conn,
                                            virDomainDefPtr domain,
                                            unsigned int flags)
    {
        virAccessManagerPtr mgr;
        int rv;

        if (!(mgr = virAccessManagerGetDefault()))
            return -1;

        if ((rv = virAccessManagerCheckDomain(mgr,
                                              conn->driver->name,
                                              domain,
                                              VIR_ACCESS_PERM_DOMAIN_WRITE)) <= 0) {
            virObjectUnref(mgr);
            if (rv == 0)
                virReportError(VIR_ERR_ACCESS_DENIED, NULL);
            return -1;
        }
        if (((flags & (VIR_DOMAIN_AFFECT_CONFIG|VIR_DOMAIN_AFFECT_LIVE)) == 0) &&
            (rv = virAccessManagerCheckDomain(mgr,
                                              conn->driver->name,
                                              domain,
                                              VIR_ACCESS_PERM_DOMAIN_SAVE)) <= 0) {
            virObjectUnref(mgr);
            if (rv == 0)
                virReportError(VIR_ERR_ACCESS_DENIED, NULL);
            return -1;
        }
        if (((flags & (VIR_DOMAIN_AFFECT_CONFIG)) == (VIR_DOMAIN_AFFECT_CONFIG)) &&
            (rv = virAccessManagerCheckDomain(mgr,
                                              conn->driver->name,
                                              domain,
                                              VIR_ACCESS_PERM_DOMAIN_SAVE)) <= 0) {
            virObjectUnref(mgr);
            if (rv == 0)
                virReportError(VIR_ERR_ACCESS_DENIED, NULL);
            return -1;
        }
        virObjectUnref(mgr);
        return 0;
    }

- 'aclsyms' - generates a linker script to export the
   APIs to drivers. Some examples

  virConnectBaselineCPUEnsureACL;
  virConnectCompareCPUEnsureACL;
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>