Revision 1044826

HTTPCLIENT-1032: variant storage now separates a "variant key" (determined by
the portion of a request covered by Vary headers on an entry) from a
"variant cache key" (the place in the cache storage where a particular variant
response is stored). The variantMap in an HttpCacheEntry now maps variant keys
to variant cache keys, setting us up for the possibility of having multiple
variant keys point to the same variant cache entry.