The keys of the hash are original file names, the values are new file
names. Originals are renamed, and then installed under the new name.

Also rearrange and alphabetise.

Fixes Homebrew/homebrew#807; Fixes Homebrew/homebrew#808

Justification:
* LLVM is too immature, it often fails to compile, sometimes irreproducibly
* The performance of the resulting bytecode is often slower than the GCC
  equivalent (eg MySQL)

If you want to continue using LLVM you can. Set HOMEBREW_USE_LLVM or brew with
--use-llvm.

We also now use the default compiler for each platform. So GCC 4.2 on Snow and
GCC 4.0 on Leopard. This also means that new formula are more likely to just
work as many over complicated build systems get upset when you mix things up.

I also did a bunch more new research regarding compiler flags. We now set the
right -march for nehalem procs and don't add redundant flags like msse3 (which
is automatically applied for all the -march settings we use).

Reducing the number of cflags will improve the overall reliability of our
platform.

If you have a bunch of symlinks and they all point at one file and you use Pathname.install on them all the error checking would fail if the file was moved before the symlinks because the symlinks would then point at a non existent file.