ENH: improve numpy.all()/any()

Unroll the loop once and use pminub/pmaxub to save a slow pmovmskb
instruction. Improves performance by 50% on some AMD chips.
Also add a pure libc path using memcmp and memchr for non amd64 systems.
The libc path can be faster with a very modern cpu and libc version,
e.g. an i7 with glibc 2.17 is about 20% faster than our code but many
other tested platforms are much slower (2.12 xeon, core2duo) or same
speed (2.17 phenom).
The numpy code can be removed in future when faster libc versions and
cpus are more commonly available.