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The main change is that, rather than using "xargs ar" we now put
all the filenames into a file, and do "ar @file". This means that
ar adds all the files at once, which works around a problem where
files with the same basename in a later invocation were overwriting
the existing file in the .a archive.

Accidnetally pushed this patch which, while it validates, isn't
correct.

rolling back:

Fri Mar 19 11:21:27 GMT 2010  Simon Marlow <marlowsd@gmail.com>
  * slight improvement to scavenging of update frames when a collision has occurred

    M ./rts/sm/Scav.c -19 +15

This makes the RTS hooks work when doing dynamic linking

Fix two places where we were doing foldl instead of foldr
after decomposing a Kind.  Strange that the same bug appears
in two quite different places!

Fixes a rare crash in the parallel GC.

If we copy a closure non-atomically during GC, as we do for all
immutable values, then before writing the forwarding pointer we better
make sure that the closure itself is visible to other threads that
might follow the forwarding pointer.  I imagine this doesn't happen
very often, but I just found one case of it: in scavenge_stack, the
RET_FUN case, after evacuating ret_fun->fun we then follow it and look
up the info pointer.

You can now link with
    -with-rtsopts="-H128m -K1m"

If RTS options are disabled then:
* The ghc_rts_opts C code variable is processed as normal
* The GHCRTS environment variable is ignored and, if it is defined, a
  warning is emitted
* The +RTS flag gives an error and terminates the program

This replaces some complicated locking schemes with message-passing
in the implementation of throwTo. The benefits are

 - previously it was impossible to guarantee that a throwTo from
   a thread running on one CPU to a thread running on another CPU
   would be noticed, and we had to rely on the GC to pick up these
   forgotten exceptions. This no longer happens.

 - the locking regime is simpler (though the code is about the same
   size)

 - threads can be unblocked from a blocked_exceptions queue without
   having to traverse the whole queue now.  It's a rare case, but
   replaces an O(n) operation with an O(1).

 - generally we move in the direction of sharing less between
   Capabilities (aka HECs), which will become important with other
   changes we have planned.

Also in this patch I replaced several STM-specific closure types with
a generic MUT_PRIM closure type, which allowed a lot of code in the GC
and other places to go away, hence the line-count reduction.  The
message-passing changes resulted in about a net zero line-count
difference.

We were getting a bogus claim that a newtype "data constructor" was
unused.  The fix is easy, although I had to add a field to the constructor
TcEnv.NewTypeDerived

See Note [Newtype deriving and unused constructors] in TcDeriv

While I was looking at the rule binders generated in DsBinds for specialise pragmas,
I also looked at Specialise.  It too was "cloning" the dictionary binders including
their IdInfo. In this case they should not have any, but its seems better to make
them completely fresh rather than substitute in existing (albeit non-existent) IdInfo.

When DsBinds deals with a SPECIALISE pragma, it makes up the binders
for a RULE. These binders should be very vanilla: no IdInfo of any sort.
But the way it was before they could have DFun pragmas, which led to
Bad Joss downstream.  (Actually to cause a downstream *error* was itself
a bug, which I've fixed, but it's clearly wrong for them to be DFuns!)

isClosedUnfolding should say False for DFUnUnfolding!

We were getting "INLINEALWAYS" printed out here and there.
Now there are always brackets around the activation, thus "INLINE[ALWAYS]"

The idea is that this leaves Tasks and OSThread in one-to-one
correspondence.  The part of a Task that represents a call into
Haskell from C is split into a separate struct InCall, pointed to by
the Task and the TSO bound to it.  A given OSThread/Task thus always
uses the same mutex and condition variable, rather than getting a new
one for each callback.  Conceptually it is simpler, although there are
more types and indirections in a few places now.

This improves callback performance by removing some of the locks that
we had to take when making in-calls.  Now we also keep the current Task
in a thread-local variable if supported by the OS and gcc (currently
only Linux).