Merge remote-tracking branch 'remotes/armbru/tags/pull-monitor-2018-07-03-v2' into staging

Monitor patches for 2018-07-03

# gpg: Signature made Tue 03 Jul 2018 22:20:13 BST
# gpg:                using RSA key 3870B400EB918653
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>"
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>"
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-monitor-2018-07-03-v2: (32 commits)
  qapi: Polish command flags documentation in qapi-code-gen.txt
  monitor: Improve some comments
  qmp: Clean up capability negotiation after commit 02130314d8c
  qobject: Let qobject_from_jsonf() fail instead of abort
  qmp: Switch timestamp_put() to qdict_from_jsonf_nofail()
  qmp: Add some comments around null responses
  qmp: Simplify monitor_qmp_respond()
  qmp: Replace get_qmp_greeting() by qmp_greeting()
  qmp: Replace monitor_json_emitter{,raw}() by qmp_{queue,send}_response()
  qmp: Use QDict * instead of QObject * for response objects
  qmp: De-duplicate error response building
  qobject: New qdict_from_jsonf_nofail()
  monitor: Peel off @mon_global wrapper
  monitor: Rename use_io_thr to use_io_thread
  qmp: Don't let JSON errors jump the queue
  qmp: Don't let malformed in-band commands jump the queue
  tests/qmp-test: Demonstrate QMP errors jumping the queue
  qmp: Simplify code around monitor_qmp_dispatch_one()
  qmp: Always free QMPRequest with qmp_request_free()
  qmp: Revert change to handle_qmp_command tracepoint
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>