dbus 1.5.x branch open for business

[Simon McVittie]

I've made the first couple of commits in master that diverge from dbus-1.4.
When preparing branches, please consider where to branch from:

- features and intrusive changes that won't be in 1.4.x should branch from
  master
- isolated bugfixes should branch from dbus-1.4

Thanks,
    S