VPN Guest support PPTP etc

[hanasaki]

Please support PPTP and other vpn's in the client. looking for options like

1. host is not on vpn - guest (windows/linux) can open its own vpn to a server while on a NAT or Host interface networking (gets its own IP)
2. host is on vpn - guest automatically uses the vpn the host is on
   • this works in vmware

A big business driver for this is the case where I have developers that are remote and need to access the internal network from a "canned" "turnkey" development environment provide by an virtual machine image (windows and linux are in use - ie: would be the guest) generally on a windows host however linux hosts are possible.

• not really sure if this should be a defect or enhancement. In either case it is desirable and also shows up in:

​http://www.virtualbox.org/ticket/1830 ​http://www.virtualbox.org/ticket/1756 ​http://www.virtualbox.org/ticket/360

• note the manual - section 6 - says that the GRE will not work on a NAT interface... It also does not work on host interface networking (which would be a work around for now...) NAT is needed because there are times the remote folks are using a wireless PHONE card which will only provide a single IP via dhcp.