QtDBus was the main component of xswiftbus' Qt dependency. This is the
first preparation step to get xswiftbus Qt free.
The new implementation is based on the low level libdbus library, which
was also in use by QtDBus itself. But instead of QtDBus, we use now a thin
C++ wrapper. To keep DBus handling async, libevent is used to monitor
timeouts and fds.
Summary:
I wanted to rename xbus because its relation to //swift// is not immediately clear from the name.
xswiftbus seems reasonable.
Reviewers: #swift_pilot_client, kbasan
Reviewed By: kbasan
Subscribers: kbasan, jenkins
Tags: #swift_pilot_client
Differential Revision: https://dev.swift-project.org/D14
