Flymake and backends exchange hints abouts changed regions

Flymake and backends exchange hints abouts changed regions

* lisp/progmodes/flymake.el (flymake--delete-own-overlays): Accept
BEG and END.  Rename from flymake-delete-own-overlays.
(flymake-diagnostic-functions): Describe :region, :recent-changes
in docstring.
(flymake--handle-report): Accept REGION.
(flymake--run-backend): Accept optional ARGS to pass to backend
fn.
(flymake--recent-changes): New buffer-local variable.
(flymake-start): Call flymake--run-backend with recent changes.
(flymake-mode): Initialize flymake--recent-changes.  Call
flymake--delete-own-overlays.
(flymake-after-change-function): Collect recent changes.

* doc/misc/flymake.texi (Backend functions): Describe
:recent-changes and :region.

* etc/NEWS (Flymake): Mention improvements in backend communication.