Add a trace mode to generate sequence UML diagram of listeners

Having a way to generate sequence UML diagram for http thread and async listeners and other worker threads will enable to :

• understand concurrency problem
• fix listeners priorities
• tune the size of pool of workers

Possible solutions

• jtracert: does not work on java7, class view and not thread view
• btrace script to extract plantuml info: not enough granularity
• add log to produce plantuml script

The last one works.
–
You can now add this on your log4j.xml:

   <category name="org.nuxeo.common.logging">
      <priority value="DEBUG" />
    </category>

Then use the sequence.sh to generate a PNG.

Note that all event in the chart are in chronological order (not proportional) except for the Initiate link where the origin point to the thread that has generated a work without telling when (earlier for sure).