how to merge dirk-thread-factorization-branch

[Dirk Herrmann <dirk at ida dot ing dot tu-bs dot de>]

Hello everybody.

Now that 1.4 is out it may be the right time to merge existing changes
into guile.  However, I don't know how to deal with this in the right
way:  There are some changes in that branch that are usefull and don't
really depend on everything else being changed, for example changes to the
test suite.  Does it make sense to incorporate such changes into the head
branch separately or is it better to merge everything in one step?

The rest of the changes form one comparably big (but not too
complicated) thing that seems to work alright, but since I am no thread
guru I'd like somebody to take a look at it and may give comments
especially about certain questions that are written as FIXME comments into
the code.

Best regards
Dirk