More RBC cleanup.

Remove extra .good and .prediff, and update comment.
Update default RBC test size so correctness testing runs faster.

Perf testing will still use the original problem size from the paper.
Merge branch 'master' of github.com:chapel-lang/chapel into rbc-fixes
Remove valgrind skipif for RBC test.

Now that the correctness test grid size is smaller, valgrind testing does not timeout.
Merge pull request #211 from thomasvandoren/rbc-fixes

Update RBC test to use smaller grid size for correctness testing.

Timeouts occurred when running the RBC test with comm. This reduces the grid size for correctness testing to reduce the execution time.

Testing:

* [x] correctness test with default config (`start_test test/studies/rbc/tvandoren/`)
* [x] correctness test with comm = gasnet (verify does not timeout) (`CHPL_COMM=gasnet SSH_SERVERS=chap11 SSH_OPTIONS=-q start_test test/studies/rbc/tvandoren/`)
* [x] correctness test with valgrind (verify does not timeout) (`start_test --valgrind test/studies/rbc/tvandoren/`)

reviewed by @mppf