"git config --list" output was hard to parse when values consist of
multiple lines. "--name-only" option is added to help this.
* sg/config-name-only:
get_urlmatch: avoid useless strbuf write
format_config: simplify buffer handling
format_config: don't init strbuf
config: restructure format_config() for better control flow
completion: list variable names reliably with 'git config --name-only'
config: add '--name-only' option to list only variable names
fc9dfda1be