Alpha-rename abort() to setAbortFlag() to distinguish it from system abort.
Added Spew of whether bailout was due to GC request or something else.

To do this, I am using the ParallelResult enum as a channel to pass
this information along to the ParallelDo.  Added "TP_RETRY_AFTER_GC",
a subcategory of "TP_RETRY_SEQUENTIALLY", to the enum to enable
printing the reasion for a GC bailout.
Merge pull request #3 from pnkfelix/spew-on-gc-bailout

Spew on gc bailout