When the clock runs out on 2007, Boston will quietly mark the end of one of the most tumultuous eras in the city's history: The Big Dig, the nation's most complex and costliest highway project, will officially come to an end. After a history marked by engineering triumphs, tunnels leaks, epic traffic jams, last year's death of a motorist crushed by falling concrete panels and a price tag that soared from $2.6 billion to a staggering $14.8 billion, there's little appetite for celebration. Civil and criminal cases stemming from the July 2006 tunnel ceiling collapse continue, though on Monday the...