http/range: reassemble files from different flows with range

http/range: reassemble files from different flows with range

adds a container, ie a thread safe hash table whose
key is the filename

keep a tree of unordered ranges, up to a memcap limit

adds HTPFileOpenWithRange to handle like HTPFileOpen
if there is a range : open 2 files, one for the whole reassembled,
and one only for the current range