completion: add hack to enable file mode in bash < 4

This way we don't need all the compat stuff, different filters, and so
on. Also, now we complete exactly the same in bash 3 and bash 4.

This is the way bash-completion did it for quite some time, when bash 3
was supported. For more information about the hack:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=272660#64

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Felipe Contreras

contrib/completion/git-completion.bash

@@ -254,49 +254,28 @@ __gitcomp_file ()
 	# completion will be used.
 	__gitcompadd "$1" "${2-}" "${3-$cur}" ""
 
-	# Tell Bash that compspec generates filenames.
-	compopt -o filenames 2>/dev/null
+	# use a hack to enable file mode in bash < 4
+	compopt -o filenames 2>/dev/null ||
+	compgen -f /non-existing-dir/ > /dev/null
 }
 
-__git_index_file_list_filter_compat ()
-{
-	local path
-
-	while read -r path; do
-		case "$path" in
-		?*/*) echo "${path%%/*}/" ;;
-		*) echo "$path" ;;
-		esac
-	done
-}
-
-__git_index_file_list_filter_bash ()
+# Process path list returned by "ls-files" and "diff-index --name-only"
+# commands, in order to list only file names relative to a specified
+# directory, and append a slash to directory names.
+__git_index_file_list_filter ()
 {
 	local path
 
 	while read -r path; do
 		case "$path" in
 		?*/*)
-			# XXX if we append a slash to directory names when using
-			# `compopt -o filenames`, Bash will append another slash.
-			# This is pretty stupid, and this the reason why we have to
-			# define a compatible version for this function.
 			echo "${path%%/*}" ;;
 		*)
 			echo "$path" ;;
 		esac
 	done
 }
 
-# Process path list returned by "ls-files" and "diff-index --name-only"
-# commands, in order to list only file names relative to a specified
-# directory, and append a slash to directory names.
-__git_index_file_list_filter ()
-{
-	# Default to Bash >= 4.x
-	__git_index_file_list_filter_bash
-}
-
 # Execute 'git ls-files', unless the --committable option is specified, in
 # which case it runs 'git diff-index' to find out the files that can be
 # committed.  It return paths relative to the directory specified in the first
@@ -2651,14 +2630,6 @@ if [[ -n ${ZSH_VERSION-} ]]; then
 
 	compdef _git git gitk
 	return
-elif [[ -n ${BASH_VERSION-} ]]; then
-	if ((${BASH_VERSINFO[0]} < 4)); then
-		# compopt is not supported
-		__git_index_file_list_filter ()
-		{
-			__git_index_file_list_filter_compat
-		}
-	fi
 fi
 
 __git_func_wrap ()