[MERGE] acl support for range_offset_limit

Here is the patch to add acl support to range_offset_limit. It is being
parsed using the same data types as reply_body_max_size, which means the
limit value gets run through parseBytesLine64, and the acl is optional.
If people are using the old global style of range_offset_limit, they
shouldn't have to do anything to their configs.

As per Amos' request, getRangeOffsetLimit is now a member of
HttpRequest, and it caches it's value the same way reply_body_max_size does.

Sorry it has taken me so long! Thanks for being patient.