Style nit
The assert that triggered in #1363 was to restrictive.

Fixes #1363
Try to explain to static checkers that we know what we're doing.
Inspired by #1356:  Make handling of req.body much more robust and
RFC-compliant.

Fixes #1356
Integrate (with minor polishing) patch from Geoff to add a SLT_BereqEnd
record with timing info about the fetch.

Submitted by: Geoff Simmons @ UPLEX