added new gather behaviour to porting guide

also removed redundant header from changelog from merge

CHANGELOG.md

@@ -27,7 +27,6 @@ Ansible Changes By Release
 * callbacks now have access to the options with which the CLI was called
 * debug is now controlable with verbosity
 
-## 2.0 "Over the Hills and Far Away"
 ## 2.0.1 "Over the Hills and Far Away"
 
 * Fixes a major compatibility break in the synchronize module shipped with

docsite/rst/porting_guide_2.0.rst

@@ -83,6 +83,8 @@ uses key=value escaping which has not changed.  The other option is to check for
 * Extras callbacks must be whitelisted in ansible.cfg. Copying is no longer necessary but whitelisting in ansible.cfg must be completed.
 * dnf module has been rewritten. Some minor changes in behavior may be observed.
 * win_updates has been rewritten and works as expected now.
+* from 2.0.1 onwards, the implicit setup task from gather_facts now correctly inherits everything from play, but this might cause issues for those setting
+  `environment` at the play level and depending on `ansible_env` existing. Previouslly this was ignored but now might issue an 'Undefined' error.
 
 Deprecated
 ----------