Merge branch 'fg/completion-external'

The command line completion mechanism (in contrib/) learned to load
custom completion file for "git $command" where $command is a
custom "git-$command" that the end user has on the $PATH when using
newer version of bash.

* fg/completion-external:
  completion: load completion file for external subcommand

Author: gitster

contrib/completion/git-completion.bash

@@ -3073,10 +3073,17 @@ __git_support_parseopt_helper () {
 __git_complete_command () {
 	local command="$1"
 	local completion_func="_git_${command//-/_}"
-	if declare -f $completion_func >/dev/null 2>/dev/null; then
+	if ! declare -f $completion_func >/dev/null 2>/dev/null &&
+		declare -f _completion_loader >/dev/null 2>/dev/null
+	then
+		_completion_loader "git-$command"
+	fi
+	if declare -f $completion_func >/dev/null 2>/dev/null
+	then
 		$completion_func
 		return 0
-	elif __git_support_parseopt_helper "$command"; then
+	elif __git_support_parseopt_helper "$command"
+	then
 		__git_complete_common "$command"
 		return 0
 	else