[krbdev.mit.edu #7872] GSS krb5 sequence number checking fails on initial gap token

[Greg Hudson via RT]

Text from a pull request by Tomas Kuthan <tkuthan at gmail.com>:
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g_order_check() fails iff first token arrives out-of-order
    
After the queue was re-written to store deltas from firstnum, the first 
(dummy) element was changed from firstnum-1 to (-1 & mask).  Now, when 
the firstnum arrives out of order, it should be inserted between the 
dummy element and the element that arrived first.  But its delta from 
firstnum is zero, which is not greater that the value of dummy element 
(all ones binary).  It doesn't fit in any other place in the queue 
either, and g_order_check returns GSS_S_FAILURE, which (according to the 
comment) should never happen.
    
To reproduce:     2 - 1 - 3
Expected outcome: GSS_S_GAP_TOKEN, GSS_S_UNSEQ_TOKEN, GSS_S_COMPLETE
Actual outcome:   GSS_S_GAP_TOKEN, GSS_S_FAILURE, GSS_S_COMPLETE
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Ticket #2040 is where util_order.c was changed to store relative 
sequence numbers in the queue, introducing this bug.