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Previously, using target HscNothing resulted in unnessesary
recompilation because 'upsweep_mod' treated HscInterface specially.
This patch changes relaxes this.

When running GHC with debug level 5, 'upsweep_mod' will now also be
more verbose about what it is doing.

There is (at least) one possible remaining problem, though: When using
target 'HscNothing' we generate a fake linkable to signal that we have
processed a module.  When switching to 'HscInterpreted' this may cause
objects to not be recompiled.  Switching from HscNothing to
HscInterpreted is therefore only safe if we unload everything first.

The problem occurred when a thread tries to GC during shutdown.  In
order to GC it has to acquire all the Capabilities in the system, but
during shutdown, some of the Capabilities have already been closed and
can never be acquired.

The recent_activity flag was an unsigned int, but we sometimes do a
64-bit xchg() on it, which overwrites the next word in memory.  This
happened to contain the sched_state flag, which is used to control the
orderly shutdown of the system.  If the xchg() happened during
shutdown, the scheduler would get confused and deadlock.  Don't you
just love C?

Fixes win32002(ghci)

Previously we only did this for references from object files, but we
should do it for all symbols, including those that GHCi looks up due
to FFI calls from bytecode.

saves a bit of memory in major GCs

The i386 native code generator has to arrange that the FPU stack is
clear on exit from any function that uses the FPU.  Unfortunately it
was getting this wrong (and has been ever since this code was written,
I think): it was looking for basic blocks that used the FPU and adding
the code to clear the FPU stack on any non-local exit from the block.
In fact it should be doing this on a whole-function basis, rather than
individual basic blocks.

ghc-pkg doesn't understand the old syntax any more, so 'ghc-pkg -l' fails

I don't think errors during dependency analysis should be passed to
the logger.

This function returns a list of all modules available through the
package DB.

MERGE TO 6.10

The sense of the #ifdef was wrong

lost in patch "Run sparks in batches"

Fixes "invalid what_next field" in ioref001 on Windows, and perhaps others

Signficantly reduces the overhead for par, which means that we can
make use of paralellism at a much finer granularity.