mk/config.mk.in : Add powerpc-unknown-linux to NoSharedLibsPlatformList.

Dynamic libraries on powerpc linux are currently broken.
See: http://hackage.haskell.org/trac/ghc/ticket/8024
.gitignore : Add libffi-tarballs.
Added support for writing and checking closed type families is hs-boot files.

As documented in the users' guide, you can now write

type family Foo a where ..

in a hs-boot file to declare an abstract closed type family.
sync-all : Replace '~~' operator with something supported by older Perl.
Rename SSE -> XMM for consistency.

We were using SSE is some places and XMM in others. Better to keep a consistent
naming scheme.
Only use real XMM registers when assigning arguments.

My original change to the calling convention mistakenly used all 6 XMM
registers---which live in the global register table---on x86 (32 bit). This
royally screwed up the floating point code generated for that platform because
floating point arguments were passed in global registers instead of on the
stack!