Hello-

What would you think about applying the following patch?

It is a standalone test that, in effect, checks to see if
BDW-GC is running marking in its own non-Guile thread.  If
BDW does have parallel marking enabled, this test will SEGV.
If it doesn't have parallel marking enabled, this test will pass.

If you run it with GC_MARKERS=1 in the env it will always
pass even if BDW-GC was compiled with parallel marking enabled.

It could be a precursor to another patch that forces GC_MARKERS=1
either in libguile or in guile.c.

Thanks,

Mike Gran