Add -fspec-inline-join-points to SpecConstr

Add -fspec-inline-join-points to SpecConstr

This patch addresses a problem that Roman found in SpecConstr.  Consider:

foo :: Maybe Int -> Maybe Int -> Int
foo a b = let j b = foo a b
           in
           case b of
             Nothing -> ...
             Just n  -> case a of
                          Just m  -> ... j (Just (n+1)) ...
                          Nothing -> ... j (Just (n-1)) ...

We want to make specialised versions for 'foo' for the patterns
	Nothing  (Just v)
	(Just a) (Just b)

Two problems, caused by the join point j.  First, j does not
scrutinise b, so j won't be specialised f for the (Just v) pattern.
Second, j is defined where the free var 'a' is not evaluated.

Both are solved by brutally inlining j at its call sites.  This risks
major code bloat, but it's relatively quick to implement.  The flag
	-fspec-inline-join-points
causes brutal inlining for a
	non-recursive binding
	of a function
	whose RHS contains calls
	of a recursive function

The (experimental) flag is static for now, and I have not even
documented it properly.