The VHD sequence validation code was erroneously counting `swap.vhd`, which caused it to raise an exception when a corresponding numbered VHD was not found. The fix is to simply ignore the `swap.vhd` file. Other unknown VHDs will generate an exception, but from a sanity-checking perspective, this is a Good Thing(tm). Fixes bug 1030939 Change-Id: Ic82ae27a4af7ea8f7669fd006aea1a310b691218