Merge branch 'date-rfc1123'

Follow RFC2616 (Date header should be in RFC1123 format).

But to reproduce this bug, program that uses libevent http-server should
call `setlocale(LC_ALL, "")` to properly initliaze locale, so that
strftime() retruns locale-specific dates.

* date-rfc1123:
  add tests for evutil_date_rfc1123().
  http: do not use local settings for Date header

Closes: #417