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