- Added transaction stats for pkgs on hold.
- Always add packages on hold to the transaction dictionary,
its type will be set to XBPS_TRANS_HOLD.
- Changed xbps_transaction_update_pkg() to have a new "force"
bool argument to force an update with a pkg on hold.
- As discussed in #274 with @Duncaen the only way to update a
pkg on hold is by using `-f`, i.e `xbps-install -f foo`.
Closes#265Closes#274