Discuss the possibility of naming threads.

This pull request is to debate the possibility of naming threads using  ``pthread_setname_np`` or   ``pthread_set_name_np`` in BSDs.

In Linux we need to use  ``#define _GNU_SOURCE`` to use  ``pthread_setname_np``. I don't know If the best approach is to do in configure.ac for all the files or put in plugin.c.

The advantage of naming threads is that in a top you can see by the name of the thread if some plugin that create threads is consuming to much cpu, or see the behaviour of readers and writers.