BIT-1240: Fix MIME entity file data/gap ordering.

MIME entities buffered data and passed it along to protocol analyzers in
discrete amounts, but a gap is always passed along right away, so the
ordering of these "events" can cause incorrect file analysis.  The
change here is to never leave any MIME data buffered -- it should now be
passed along line by line as it is seen, but may still temporarily make
use of a buffer allocated by the analyzer as it works on decoding
content.
Implement file ID caching for MIME_Mail.
Raise http_entity_data in line with data arrival.

As opposed to delaying until a certain-sized-buffer fills, which is
problematic because then the event becomes out of sync with the "rest of
the world".  E.g. content_gap handlers being called sooner than
expected.

Addresses BIT-1240.
Fix issue w/ TCP reassembler not delivering some segments.

For example, if we have a connection between TCP "A" and TCP "B" and "A"
sends segments "1" and "2", but we don't see the first and then the next
acknowledgement from "B" is for everything up to, and including, "2",
the gap would be reported to include both segments instead of just the
first and then delivering the second.  Put generally: any segments that
weren't yet delivered because they're waiting for an earlier gap to be
filled would be dropped when an ACK comes in that includes the gap as
well as those pending segments.  (If a distinct ACK was seen for just
the gap, that situation would have worked).

Addresses BIT-1246.
Fix file analysis placement of data after gap in HTTP Content-Range.

Addresses BIT-1248.
Fix incorrect data delivery skips after gap in HTTP Content-Range.

The logic for determining whether a gap was entirely within a MIME
entity body was not asking the current entity, which may be better able
to answer that question if it was using the Content-Range header and
thus knows if the gap exceeds the length of the body that's still
expected.

Addresses BIT-1247
Merge remote-tracking branch 'origin/topic/jsiwek/jj-bugs'

* origin/topic/jsiwek/jj-bugs:
  Fix incorrect data delivery skips after gap in HTTP Content-Range.
  Fix file analysis placement of data after gap in HTTP Content-Range.
  Fix issue w/ TCP reassembler not delivering some segments.
  Raise http_entity_data in line with data arrival.
  Implement file ID caching for MIME_Mail.
  BIT-1240: Fix MIME entity file data/gap ordering.

BIT-1240 #closed
BIT-1246 #closed
BIT-1247 #closed
BIT-1248 #closed