- Don't make vgonel() globally visible, we want to change its prototype

 - Don't make vgonel() globally visible, we want to change its prototype
   anyway and it's not used outside of vfs_subr.c.
 - Change vgonel() to accept a parameter which determines whether or not
   we'll put the vnode on the free list when we're done.
 - Use the new vgonel() parameter rather than VI_DOOMED to signal our
   intentions in vtryrecycle().
 - In vgonel() return if VI_DOOMED is already set, this vnode has already
   been reclaimed.

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