-nobar option: no progress bar
process (Int64 i)

When i is biggger than the maximum int value of OCaml, Cil.i64_to_int
raises an exception.  So, I modified eval_const function to return
Itv.top in the case.
modified frontend to be consistent about nodes

old: Some nodes in cmd_map did not exist in graph when they do not
have any edges.  By many functions, the result of IntraCfg.nodesof is
treated as the whole nodes, but IntraCfg.nodesof only returns the
nodes included in the graph.

now: Every node in the cmd_map is also included in the graph even when
it does not have any edges.  In that case, the nodes will be removed
later by unreachable node detection.
Merge branch 'master' of github.com:skcho/zooberry