[pca] concurrent download threads

[Martin Paul]

I just put a new development release of pca online, with this change:

  * Add option for concurrent patch downloads (--threads=NUM)

It's a rather big change in code actually - I've finally integrated the 
patch by Chris Reece which he made available at:

   http://www.sparsezone.com/pca/

It adds the functionality to download multiple patches from SunSolve in 
parallel. This can speedup downloads of big patch sets dramatically. You 
will need a perl with threading support compiled in (Solaris' 
/usr/bin/perl unfortunately doesn't have it). "pca --help" or "perl 
-V:useithreads" will tell you about threads support in your copy of perl.

Kudos to Chris, who has been supporting and developing the patch over a 
long time, and has been listening to every proposal I made to make the 
patch integrate smoothly.

Martin.