virtualbox: Update to version 4.3.26.

Upstream changelog:

 * GUI: in the snapshots pane, protect the age of snapshots against
        wrong host time
 * NAT Network: fixed a bug which prevented to propagate any DNS name
                server / domain / search string information to the NAT
                network (4.3.24 regression)
 * NAT Network: don't delay the shutdown of VBoxSVC on Windows hosts
 * Mouse support: the mouse could not be moved under rare conditions if
                  no Guest Additions are installed (4.3.24 regression)
 * Storage: if the guest ejects a virtual CD/DVD medium, make the change
            permanent
 * VGA: made saving secondary screen sizes possible in X11 guests
 * SDK: fixed the VirtualBox.tlb file (4.3.20 regression)
 * rdesktop-vrdp: make it work with USB devices again (4.3.14
                  regression)
 * USB: fixed a possible BSOD on Windows hosts under rare conditions
 * iPXE: enable the HTTP download protocol on non-Linux hosts
 * Mac OS X hosts: don't panic on hosts with activated SMAP (Broadwell
                   and later)
 * Linux hosts: don't crash Linux 4.0 hosts

The same with bug IDs can be found at:

https://www.virtualbox.org/wiki/Changelog



Tested on my machine using the virtualbox NixOS VM test.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>