Framework for supporting SIMD acceleration

Designed to impose minimal changes on the "normal" code.
Implement x86 SIMD framework

Add NASM support and stub routine for detecting SIMD extensions.
"Optimise" quantization step by replacing the division by a multiplication.

This has no measurable difference right now but makes it possible to do
SIMD implementations of this stage.
Add MMX SIMD implementation of computationally intensive routines.
Add 3DNow SIMD implementation of computationally intensive routines.
Make sure the work space memory is properly aligned

We use the heap allocators to avoid having more than one implementation
of the alignment logic.
Most SIMD implementations need 16 byte alignment
Add SSE SIMD implementation of computationally intensive routines.
Add SSE2 SIMD implementation of computationally intensive routines.
Import autogenerated files for unix/ and common/ subdirs to make source
compilable without GNU autotools.
Include Huffman codec optimizations borrowed from TurboJPEG
Don't mix LOCAL() and qualifiers.
Move variable init around a bit to please crappy compilers.
Add new simd files to Visual Studio project file.
Revert r3657 (import of autogenerated) files.
Make source compilable via GNU autotools which are part of RHEL 5.
Fix broken buffered I/O (to make cjpeg work)
Work around subdirectory bug in older automake.

Older versions of automake doesn't properly support no-recursive make.
Reimplement the build system by having a local Makefile.am in the
simd/ directory.
Eliminate backward incompatibility that required empty_output_buffer() to handle cases in which the buffer wasn't 100% full
Fix build for RGB_PIXELSIZE==4