Added expectNoConsumption() BodyPipe method to allow the consumer side to

Added expectNoConsumption() BodyPipe method to allow the consumer side to
tell the pipe that no more consumers are expected.

Calling expectNoConsumption() is needed when all consumers are gone but none
of them consumed anything. This is typical for HTTP server-side transactions
that abort before they receive the adapted ICAP request body. If FwdState
quits without calling expectNoConsumption(), the ICAP transaction supplying
the request body may get stuck waiting for buffer space. The body pipe may be
the ICAP only link with the master transaction once the header is handled.

This change is related to Squid bug #2964.
Based on lp 3p1-rock branch, r9609.