When counting memory from closing a connection, count the dir conn too

Fix part of bug 11972
Count zlib buffer memory towards OOM totals.

Part of 11792.

(Uses the zlib-endorsed formula for memory needs for inflate/deflate
from "zconf.h".)
Kill non-tunneled directory connections when handling OOM.

Another part of 11792.
When looking for conns to close, count the age of linked queued data

Specifically, count the age of the data queued in a linked directory
connection's buffers when counting a stream's age.
Merge branch 'bug11792_1_squashed'

Conflicts:
	src/or/circuitlist.c