All vbox objects are child objects from the nsISupports in vbox's
C++ API version. Since the CAPI is generated from the C++ API, I
kept their relationship here, by the definitations below:

typedef struct nsISupports nsISupports;
typedef nsISupports IVirtualBox;
typedef nsISupports ISession;
and so on...

So, when calling the API from nsISupports, we don't need to do
typecasting, and things work still work well.

Introduce vbox_uniformed_api to deal with version conflicts. Use
vbox_install_api to register the currect vboxUniformedAPI with
vbox version.

vboxConnectOpen has been rewritten.

Martin Kletzander pointed out in email that my commit 2a193f64
introduced a crash in networkCreateInterfacePool() during startup of
any network that doesn't have a <pf> subelement of its <forward>
element. He also supplied a patch.

 http://www.redhat.com/archives/libvir-list/2014-August/msg00655.html

I expanded on that patch by cleaning up now-extraneous checks in the
callers of networkCreateInterfacePool().

Fortunately the offending patch hasn't been in any release, and hasn't
been (to my knowledge) backported to any other branch.

Handle formating of VIF config in a new function xenFormatXMVif().
Signed-off-by: NKiarie Kahurani <davidkiarie4@gmail.com>