[LuaJIT] jit.p: Enhance 'v' profiler mode

[lukego]

This change prints more information when profiling at trace granularity. The idea is to make it easier to audit the runtime behavior of your apps: how many traces do they compile into, how are those traces connected together, and which execution path does each trace represent.

This PR builds on #619 and contains the code previously described in issue #611.

More detail with examples:

Previously the 'v' mode would print a terse summary. For example when profiling the rate_limiter app selftest:

    $ sudo ./snabb snsh -jdump=+rs,x -jp=v -t apps.rate_limiter.rate_limiter
    47%  TRACE 16
    22%  TRACE 15
    11%  TRACE 14
    10%  TRACE 12
     4%  TRACE 18
     4%  TRACE 24

More information is shown with this change:

    $ sudo ./snabb snsh -jdump=+rs,x -jp=v -t apps.rate_limiter.rate_limiter
    47%  TRACE  16 (14/4)   ->14       rate_limiter.lua:82
    22%  TRACE  15          ->loop     basic_apps.lua:82
    11%  TRACE  14          ->loop     rate_limiter.lua:73
    10%  TRACE  12          ->loop     basic_apps.lua:26
     4%  TRACE  18 (12/13)  ->14       basic_apps.lua:25
     4%  TRACE  24 (19/10)  ->12       app.lua:293

This tells us:

• Is this a side-trace? If so then (PARENT/EXIT) is shown.
• What does the end of the trace link to? (loop, other trace, ..?)
• What source line does the trace begin on? (Requires -jdump to be in use)

Note that it is also possible to combine this profile mode with line based profiling to have more visibility into what is happening inside traces:

    45%  TRACE  13 (10/9)   ->10       rate_limiter.lua:82
      -- 33%  counter.lua:add
      -- 32%  packet.lua:free
      -- 20%  freelist.lua:freelist_add
      -- 10%  rate_limiter.lua:method
      --  3%  link.lua:full
    21%  TRACE   8          ->loop     basic_apps.lua:26
      -- 44%  packet.lua:clone
      -- 18%  counter.lua:add
      -- 11%  packet.lua:allocate
      --  9%  freelist.lua:allocate
      --  9%  basic_apps.lua:method
      --  7%  link.lua:full
      --  4%  link.lua:transmit
    19%  TRACE  10          ->loop     rate_limiter.lua:73
      -- 58%  rate_limiter.lua:method
      -- 21%  link.lua:receive
      -- 17%  counter.lua:add
     7%  TRACE  11          ->loop     basic_apps.lua:82
      -- 74%  counter.lua:add
      -- 21%  link.lua:receive
      --  5%  packet.lua:free_internal