Fix the meaning of '=' in logexpect

Fix the meaning of '=' in logexpect to mean same value as that of the
last successfully matched log record.
Fix logexp record length to account for terminating zero.

This makes it possible to anchor regex's at the end again.
Remove struct sess acct_bit and bit fields from SessClose log record

We want to remove the req->acct_req dup counters that was feeding this
data to reduce the size of struct req. The statistics value of the
boolean flags was also small. So it's going away.
Request handling byte accounting

Counters show bytes received/transmitted, split between header and
body bytes.

SLT_ReqAcct logs per request counter values.
ESI byte accounting

Charge ESI bodybytes to the parent request.

Log SLT_ESI_BodyBytes in each ESI-involved log transaction. This shows
how many bytes each request adds to the total byte count.

SLT_ReqAcct is not logged for ESI sub-requests.
Pipe byte accounting

Add VSC counters for pipe traffic. Traffic is split between header
bytes, and input and output piped bytes.

Log SLT_PipeAcct records showing per pipe session byte counts.
Backend fetch byte accounting

Add SLT_BereqAcct log records showing headers and bodybytes
received/transmitted when doing backend fetch operations.
Backend fetch counters

Add per-backend VSC counters for traffic going in/out of this backend.
Use SLT_ReqAcct for length in varnishncsa
Use SLT_ReqAcct for length in varnishhist
Remove ReqEnd and BereqEnd vsl tags

These tags are now obsolete
clarify elements of the public VSL API