The directory-wide PREDIFF script copies the appropriate .good file
into the expected .good file.  For example, when running alloc.chpl
using the block distribution with gasnet, alloc.block.good is copied
to alloc.good for comparison during testing.  Similarly, when running
alloc.chpl using the default distribution, it copies
alloc.default.good.

You should never check in a "plain" .good file in this directory,
where plain means foo.good when the test is in a file named foo.chpl.
