[collectd] collectd 5.10 threading

[Brandon Hume]

  I'm trying to debug a plugin (not part of the distribution) that uses 
mysql to write the most recent measurements into a database.  I'm 
running it in an extremely threaded environment - Solaris on a SPARC T4 
with a crazy number of CPUs - and it crashes and gets queries out of 
sync and many other signs of a race condition.

Mysql is supposedly thread safe but you have to be careful about 
initializing the functions and coordinating queries.  So, I'm reviewing 
the code and trying to find spots where it would be tripping over itself.

At what point does collectd start threading?  Is it already spawning 
threads by the time the plugin init functions are being called?  Is it 
possible for a plugin init function to be called multiple times?