Merge branch 'mm/config-color-ui-default-to-auto' into maint

Merge branch 'mm/config-color-ui-default-to-auto' into maint

Documentation for individual configuration variables to control use
of color (like `color.grep`) said that their default value is
'false', instead of saying their default is taken from `color.ui`.
When we updated the default value for color.ui from 'false' to
'auto' quite a while ago, all of them broke.  This has been
corrected.

* mm/config-color-ui-default-to-auto:
  Documentation/config: default for color.* is color.ui