inffast64.c benchmarks

inffast64.benchmarks.txt

Speed up inflate_fast by up to 1.5x on x86_64.

https://github.com/google/snappy is an unrelated compression format but
its snappy_unittest program is able to benchmark the snappy library and
the zlib library. We can re-purpose it, via LD_LIBRARY_PATH, to measure
different versions of zlib, such as before / after this commit.

snappy_unittest's output looks like:

testdata/alice29.txt                     :
ZLIB:   [b 1M] bytes 152089 ->  54404 35.8%  comp  19.6 MB/s  uncomp 258.2 MB/s
testdata/asyoulik.txt                    :
ZLIB:   [b 1M] bytes 125179 ->  48897 39.1%  comp  17.9 MB/s  uncomp 242.9 MB/s
etc

and summarizing the before/after zlib uncompress numbers give:

alice29.txt       uncomp MB/s  before  258.2  after  392.4  ratio 1.52
asyoulik.txt      uncomp MB/s  before  242.9  after  346.6  ratio 1.43
fireworks.jpeg    uncomp MB/s  before 1066.7  after 1194.7  ratio 1.12
geo.protodata     uncomp MB/s  before  565.6  after  756.8  ratio 1.34
html              uncomp MB/s  before  492.1  after  698.8  ratio 1.42
html_x_4          uncomp MB/s  before  502.1  after  697.8  ratio 1.39
kppkn.gtb         uncomp MB/s  before  336.4  after  483.6  ratio 1.44
lcet10.txt        uncomp MB/s  before  265.2  after  409.5  ratio 1.54
paper-100k.pdf    uncomp MB/s  before  264.9  after  331.4  ratio 1.25
plrabn12.txt      uncomp MB/s  before  240.9  after  372.5  ratio 1.55
urls.10K          uncomp MB/s  before  280.7  after  381.3  ratio 1.36