MB-100 Update internalSettings in doc/api.txt.

Change-Id: I6729cdeb53711f6f3cbde7a39c8ef570a7f072c6
Reviewed-on: http://review.couchbase.org/26354
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8199 Allow keeping request throttling settings intact.

So that if certain setting is just omitted, then the old value is
used. But if the value is empty, then we set it to unlimited.

Change-Id: I5c339ed50c98b07343c12e8c2790720b3d7b5cc3
Reviewed-on: http://review.couchbase.org/26355
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
MB-8199 Prevent request_throttler from crash if it restarts.

Some of our REST endpoints restart almost all the supervision
tree. Previously note_request_done of such request would be handled
already by restarted process. This would cause it to crash and would
fail the request. To prevent this note_request returns throttler pid
as part of response. Then note_request_done uses this pid. So that new
instance of request throttler is unaffected. Additionally,
note_request_done now uses gen_server:cast instead of gen_server:call
to prevent request handlers from random request_throttler failures.

Change-Id: I9890d586fdfc25364de9153ae54925cb639a0c82
Reviewed-on: http://review.couchbase.org/26356
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>