Update/Alteration to our version of thread-ring.  I took the original file,
which had an if/else branch for using coforall versus a for loop with begin
statements for parallel task creation (even though both branches did roughly
the same thing), and split that option into three separate files: one for the
for+begin, one for a plain coforall loop, and one for a coforall loop that also
utilizes begin statements within it.  This last version performs roughly twice
as fast as the other two at the moment.  A directory demonstrating the speeds
of coforall/coforall+begin/for+begin is forthcoming.

README documents the changes, as well as other things I have tried for
performance improvements but have not/will not commit.



git-svn-id: http://svn.code.sf.net/p/chapel/code/trunk@21784 3a8e244f-b0f2-452b-bcba-4c88e055c3ca