Merge branch 'sg/config-name-only'

"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

contrib/completion/git-completion.bash

@@ -744,9 +744,8 @@ __git_compute_porcelain_commands ()
 __git_get_config_variables ()
 {
 	local section="$1" i IFS=$'\n'
-	for i in $(git --git-dir="$(__gitdir)" config --get-regexp "^$section\..*" 2>/dev/null); do
-		i="${i#$section.}"
-		echo "${i/ */}"
+	for i in $(git --git-dir="$(__gitdir)" config --name-only --get-regexp "^$section\..*" 2>/dev/null); do
+		echo "${i#$section.}"
 	done
 }
 
@@ -1777,15 +1776,7 @@ __git_config_get_set_variables ()
 		c=$((--c))
 	done
 
-	git --git-dir="$(__gitdir)" config $config_file --list 2>/dev/null |
-	while read -r line
-	do
-		case "$line" in
-		*.*=*)
-			echo "${line/=*/}"
-			;;
-		esac
-	done
+	git --git-dir="$(__gitdir)" config $config_file --name-only --list 2>/dev/null
 }
 
 _git_config ()
@@ -1890,6 +1881,7 @@ _git_config ()
 			--get --get-all --get-regexp
 			--add --unset --unset-all
 			--remove-section --rename-section
+			--name-only
 			"
 		return
 		;;