Use os:timestamp/0 instead of now/0
Do not log client disconnects as errors

In the future it would be nice to collect metrics of these, but
practically speaking we already have them in the HAProxy logs.

BugzID: 14090

Conflicts:
	src/chttpd.erl
Pull up couch_httpd:body/1
Reorder clauses to reduce diff noise
Check that a request body was sent before decoding

BugzID: 14114