Refactor construction of switch statements to avoid subgraphs.

Refactor construction of switch statements to avoid subgraphs.

Refactor construction of switch statements so it doesn't use class
HSubgraph.

There are also a few improvements.  We do not use an auxiliary list of
comparisons because they're embedded as a linked list in the graph
under construction.  We share a common break block for all breaks from
the same switch.  We do not insert empty blocks unless necessary to
maintain edge-split form.

There is also a bug fix.  The entry to a clause body is a potential
join and must have a join ID set, otherwise deoptimization within the
body can go to an unpredictable place in the unoptimized code.

Committed: http://code.google.com/p/v8/source/detail?r=7099

[fschneider, 2011-03-09 12:04:15]

LGTM.