bash_completion: try to use bash3 features if they're available

This does NOT break completion for bash 2.05b (I haven't tested
earlier versions)

contrib/bash_completion

@@ -1,169 +1,170 b''
 #!/bin/bash
 
 _hg_commands()
 {
     local commands="$(hg -v help | sed -e '1,/^list of commands:/d' \
                                        -e '/^global options:/,$d' \
 				       -e '/^ [^ ]/!d; s/[,:]//g;')"
     
     # hide debug commands from users, but complete them if 
     # specifically asked for
     if [[ "$cur" == de* ]]; then
 	commands="$commands debugcheckstate debugstate debugindex"
 	commands="$commands debugindexdot debugwalk debugdata"
     fi
     COMPREPLY=( ${COMPREPLY[@]:-} $(compgen -W "$commands" -- "$cur") )
 }
 
 _hg_paths()
 {
     local paths="$(hg paths | sed -e 's/ = .*$//')"
     COMPREPLY=(${COMPREPLY[@]:-} $( compgen -W "$paths" -- "$cur" ))
 }
 
 _hg_status()
 {
     local files="$( hg status -$1 | cut -b 3- )"
     COMPREPLY=(${COMPREPLY[@]:-} $( compgen -W "$files" -- "$cur" ))
 }
 
 _hg_tags()
 {
     local tags="$(hg tags | sed -e 's/[0-9]*:[a-f0-9]\{40\}$//; s/ *$//')"
     COMPREPLY=( ${COMPREPLY[@]:-} $(compgen -W "$tags" -- "$cur") )
 }
 
 # this is "kind of" ugly...
 _hg_count_non_option()
 {
     local i count=0
     local filters="$1"
 
     for (( i=1; $i<=$COMP_CWORD; i++ )); do
 	if [[ "${COMP_WORDS[i]}" != -* ]]; then
 	    if [[ ${COMP_WORDS[i-1]} == @($filters|$global_args) ]]; then
 		continue
 	    fi
 	    count=$(($count + 1))
 	fi
     done
 
     echo $(($count - 1))
 }
 
 _hg()
 {
     local cur prev cmd opts i
     # global options that receive an argument
     local global_args='--cwd|-R|--repository'
 
     COMPREPLY=()
     cur="$2"
     prev="$3"
 
     # searching for the command 
     # (first non-option argument that doesn't follow a global option that
     #  receives an argument)
     for (( i=1; $i<=$COMP_CWORD; i++ )); do
 	if [[ ${COMP_WORDS[i]} != -* ]]; then
 	    if [[ ${COMP_WORDS[i-1]} != @($global_args) ]]; then
 		cmd="${COMP_WORDS[i]}"
 		break
 	    fi
 	fi
     done
 
     if [[ "$cur" == -* ]]; then
 	# this assumes that there are no commands with spaces in the name
 	opts=$(hg -v help $cmd | sed -e '/^ *-/!d; s/ [^- ].*//')
 
 	COMPREPLY=( ${COMPREPLY[@]:-} $(compgen -W "$opts" -- "$cur") )
 	return
     fi
 
     # global options
     case "$prev" in
 	-R|--repository)
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -d -- "$cur" ))
 	    return
 	;;
 	--cwd)
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -d -- "$cur" ))
 	    return
 	;;
     esac
 
     if [ -z "$cmd" ] || [ $COMP_CWORD -eq $i ]; then
 	_hg_commands
 	return
     fi
 
     # canonicalize command name
     cmd=$(hg -q help "$cmd" | sed -e 's/^hg //; s/ .*//; 1q')
 
     if [ "$cmd" != status ] && [ "$prev" = -r ] || [ "$prev" = --rev ]; then
 	_hg_tags
 	return
     fi
 
     case "$cmd" in
 	help)
 	    _hg_commands
 	;;
 	export|manifest|update)
 	    _hg_tags
 	;;
 	pull|push|outgoing|incoming)
 	    _hg_paths
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -d -- "$cur" ))
 	;;
 	paths)
 	    _hg_paths
 	;;
 	add)
 	    _hg_status "u"
 	;;
 	commit)
 	    _hg_status "mra"
 	;;
 	remove)
 	    _hg_status "r"
 	;;
 	forget)
 	    _hg_status "a"
 	;;
 	diff)
 	    _hg_status "mra"
 	;;
 	revert)
 	    _hg_status "mra"
 	;;
 	clone)
 	    local count=$(_hg_count_non_option)
 	    if [ $count = 1 ]; then
 		_hg_paths
 	    fi
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -d -- "$cur" ))
 	;;
 	debugindex|debugindexdot)
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -f -X "!*.i" -- "$cur" ))
 	;;
 	debugdata)
 	    COMPREPLY=(${COMPREPLY[@]:-} $( compgen -f -X "!*.d" -- "$cur" ))
 	;;
 	cat)
 	    local count=$(_hg_count_non_option '-o|--output')
 	    if [ $count = 2 ]; then
 		_hg_tags
 	    else
 		COMPREPLY=(${COMPREPLY[@]:-} $( compgen -f -- "$cur" ))
 	    fi
 	;;
 	*) 
             COMPREPLY=(${COMPREPLY[@]:-} $( compgen -f -- "$cur" ))
 	;;
     esac
 
 }
 
-complete -o default -F _hg hg
+complete -o bashdefault -o default -F _hg hg 2> /dev/null \
+    || complete -o default -F _hg hg