* new Optional Directives
* CacheMemEntrySize -- max size of a individual entry in memory
cache
* CacheIgnoreNoLastMod - so we can cache mod-included files
* it tries to figure out the size of the request based on buckets if the
content-length header isn't set
* mem_cache now caches the subprocess_env & notes tables
* the CACHE_IN/OUT/CONDITIONAL run at FTYPE_CONTENT+1, so that
all other content filters run BEFORE the cache in.
note: the code is still experimental, and we need a bit more work
mainly...
* garbage collection
* cache stats/reporting
* manual removal of a key.