Issue #1439: Make extend option to overwrite in the right direction

Signed-off-by: Anton Kovalyov <anton@kovalyov.net>
Issue #1449: Replace for..in loops with forEach where appropriate
Issue #1451: Fix a regression caused by #1388
Issue #1123: Make checks for generator functions without yield optional
Issue #1477: Add matchMedia to the browser list of globals
Issue #1460: Fixed a typo in messages.js
Issue #1425: Add 'unknown' to the list of valid typeof values
Treat leading slash as relative to the current dir for consistency with .gitignore

Signed-off-by: Anton Kovalyov <anton@kovalyov.net>
Issue #1453: Handle single-line comments for block ignore
No issue: tabs to spaces
No issue: tabs to spaces
No issue: tabs to spaces
Issue #1456: New option - nonbsp
No issue: change message for W104