In incredibly seldom circumstances this bug would cause ESI:include
data to be bad.

Fixes:	#1852

None of it was important or troubling.

Fixes #1851.

Dump boc's in panic output

need the busyobj at all now.

Dispose when refcount goes to zero.
Private objcores for pipe neither want nor need a boc, so make it optional.

I don't think this will be necessary at the end state, but it makes
the transformation easier.

now that we have a struct boc.

(struct boc) and "the backend fetch context" (struct bereq).

WS_Assert allows the workspace to be full in its check that `ws->f <= ws->e`.
WS_Reset does not honor this; if a snapshot was taken of a full workspace, and
that snapshot is reverted with WS_Reset, we panic.

This issue was identified by Jozef Hatala <jozef@fastly.com>