Fix &trace, add "-w" option to print critical path

[eddiehung]

Example output:

abc - > &if -v -W 250;
K = 8. Memory (bytes): Truth =    0. Cut =   64. Obj =  144. Set =  672. CutMin = no
Node =    4304.  Ch =     0.  Total mem =    1.35 MB. Peak cut mem =    0.16 MB.
P:  Del = 3455.00.  Ar =    4989.0.  Edge =     5555.  Cut =    52962.  T =     0.01 sec
P:  Del = 3416.00.  Ar =    4689.0.  Edge =     5715.  Cut =    52102.  T =     0.01 sec
P:  Del = 3416.00.  Ar =    3409.0.  Edge =     4705.  Cut =    61617.  T =     0.01 sec
E:  Del = 3416.00.  Ar =    3372.0.  Edge =     4641.  Cut =    61617.  T =     0.00 sec
F:  Del = 3416.00.  Ar =    3278.0.  Edge =     4607.  Cut =    60112.  T =     0.01 sec
E:  Del = 3416.00.  Ar =    3274.0.  Edge =     4602.  Cut =    60112.  T =     0.00 sec
A:  Del = 3416.00.  Ar =    3244.0.  Edge =     4401.  Cut =    61874.  T =     0.02 sec
E:  Del = 3416.00.  Ar =    3242.0.  Edge =     4399.  Cut =    61874.  T =     0.00 sec
A:  Del = 3416.00.  Ar =    3242.0.  Edge =     4398.  Cut =    61392.  T =     0.02 sec
E:  Del = 3416.00.  Ar =    3242.0.  Edge =     4398.  Cut =    61392.  T =     0.00 sec
Total time =     0.10 sec
abc - > &trace -l -W 250 -w;
Max delay = 3416.00. Delay trace using LUT library model:
 3416.00  PO
 2701.00  LUT  (K = 8)
 2213.00  LUT  (K = 6)
 1900.00  BOX  num    95 (CARRY4)
 1786.00  BOX  num    94 (CARRY4)
 1260.00  BOX  num    93 (CARRY4)
  791.00  BOX  num    80 (CARRY4)
  303.00  LUT  (K = 2)
  303.00  PI

Note that &trace is not currently aware of muxes (produced by &if -i) nor LUT structures (&if -S NN)

Also fixes &if -w which calls the equivalent of &trace -v