branching updates

[Ben Pfaff]

I had been maintaining a branch "pre-0.6.1" to track the changes
I was making for the 0.6.1 release candidates.  Now that branch
is gone, with the changes that were on it merged into the
"stable" branch.

(John, that means that your --enable-relocatable fixes are
already pushed to stable, since I had added them to pre-0.6.1 and
hence to the 0.6.1 release.)

After that, I merged the changes from stable into master and
updated master.

Unfortunately, master doesn't build now:
               ../src/language/tests/check-model.q:24:27: error: 
model-checker.h: No such file or directory
John, you moved some model-checker files around, is this related?
-- 
"Welcome to the Slippery Slope. Here is your handbasket.
 Say, can you work 70 hours this week?"
--Ron Mansolino