Merge branch 'rs/config-set-multi-error-message-fix'

The error message given by "git config set", when the variable
being updated has more than one values defined, used old style "git
config" syntax with an incorrect option in its hint, both of which
have been corrected.

* rs/config-set-multi-error-message-fix:
  config: fix suggestion for failed set of multi-valued option

diff --cc builtin/config.c
Simple merge