1.2x to 1.9x speedup for sha1sum using SSE2

[dean gaudet]

at <http://arctic.org/~dean/crypto/sha1.html> you'll find a coreutils
patch which includes a new implementation of SHA1 using SSE2 hardware for
a speedup ranging from 1.2x to 1.9x depending on which SSE2-capable CPU is
used.

there's a complication to compiling this code -- it requires the intel
compiler for one file (gcc should compile it, but it trips a bug which has
been reported).  i've included icc-generated assembly... and a makefile
hack to use the assembly.  it's all enabled with --enable-sse2.

-dean