difftool/mergetool: add diffuse as merge and diff tool

This adds diffuse as a built-in merge tool.

Signed-off-by: Sebastian Pipping <sebastian@pipping.org>
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1174,7 +1174,8 @@ _git_mergetool ()
 	--tool=*)
 		__gitcomp "
 			kdiff3 tkdiff meld xxdiff emerge
-			vimdiff gvimdiff ecmerge opendiff
+			vimdiff gvimdiff ecmerge diffuse
+			opendiff
 			" "" "${cur##--tool=}"
 		return
 		;;

contrib/difftool/git-difftool-helper

@@ -1,7 +1,5 @@
 #!/bin/sh
 # git-difftool-helper is a GIT_EXTERNAL_DIFF-compatible diff tool launcher.
-# It supports kdiff3, kompare, tkdiff, xxdiff, meld, opendiff,
-# emerge, ecmerge, vimdiff, gvimdiff, and custom user-configurable tools.
 # This script is typically launched by using the 'git difftool'
 # convenience command.
 #
@@ -55,6 +53,10 @@ launch_merge_tool () {
 		"$merge_tool_path" "$LOCAL" "$REMOTE"
 		;;
 
+	diffuse)
+		"$merge_tool_path" "$LOCAL" "$REMOTE" | cat
+		;;
+
 	vimdiff)
 		"$merge_tool_path" -d -c "wincmd l" "$LOCAL" "$REMOTE"
 		;;
@@ -164,9 +166,9 @@ if test -z "$merge_tool"; then
 	if test -n "$DISPLAY"; then
 		# If gnome then prefer meld, otherwise, prefer kdiff3 or kompare
 		if test -n "$GNOME_DESKTOP_SESSION_ID" ; then
-			merge_tool_candidates="meld kdiff3 kompare tkdiff xxdiff gvimdiff"
+			merge_tool_candidates="meld kdiff3 kompare tkdiff xxdiff gvimdiff diffuse"
 		else
-			merge_tool_candidates="kdiff3 kompare tkdiff xxdiff meld gvimdiff"
+			merge_tool_candidates="kdiff3 kompare tkdiff xxdiff meld gvimdiff diffuse"
 		fi
 	fi
 	if echo "${VISUAL:-$EDITOR}" | grep 'emacs' > /dev/null 2>&1; then

contrib/difftool/git-difftool.txt

@@ -25,8 +25,8 @@ OPTIONS
 --tool=<tool>::
 	Use the diff tool specified by <tool>.
 	Valid merge tools are:
-	kdiff3, kompare, tkdiff, meld, xxdiff, emerge,
-	vimdiff, gvimdiff, ecmerge, and opendiff
+	kdiff3, kompare, tkdiff, meld, xxdiff, emerge, vimdiff, gvimdiff,
+	ecmerge, diffuse and opendiff
 +
 If a diff tool is not specified, 'git-difftool'
 will use the configuration variable `diff.tool`.  If the