Compile Qt with Dbus support on Linux

- This is only for Linux and with it Spyder and IPython qtconsole work correctly under KDE.
- The lack of `libQtDBus` in Anaconda makes Oxygen (the default KDE theme)
to look for it on the system, which causes an incompatible mix between
Anaconda and system Qt libraries.
- Fixes ContinuumIO/anaconda-issues#32