change hash fns for R16B01 compat
Merge pull request #155 from basho/pevm-r16-compat-rebased

change hash fns for R16B01 compat
fix R15 compatibility
Avoid DST-aware translation from localtime to GMT

httpd_util:rfc1123_date/1 uses internally erlang:localtime_to_universaltime/2
with 2nd argument of true. The function takes msec or tens of msec
depending on concurrency.

Usage of httpd_util:rfc1123_date/1 in webmachine_decision_core is
tuple style GMT -> tuple-style localtime -> RFC 1123 string (also GMT)
New utility function webmachine_util:rfc1123_date converts
tuple style GMT to RFC 1123 string directly.
Add last_modified callback
Merge pull request #156 from basho/pevm-fix-R15

fix R15 compatibility
Merge pull request #158 from basho/ss-avoid-localtime-to-universaltime

Avoid localtime to universaltime