Merge branch 'th/difftool-diffall'

Rolls the two-directory-diff logic from diffall script (in contrib/) into
"git difftool" framework.

By Tim Henigan
* th/difftool-diffall:
  difftool: print list of valid tools with '--tool-help'
  difftool: teach difftool to handle directory diffs
  difftool: eliminate setup_environment function
  difftool: stop appending '.exe' to git
  difftool: remove explicit change of PATH
  difftool: exit(0) when usage is printed
  difftool: add '--no-gui' option
  difftool: parse options using Getopt::Long

Author: gitster

Documentation/git-difftool.txt

@@ -19,6 +19,12 @@ linkgit:git-diff[1].
 
 OPTIONS
 -------
+-d::
+--dir-diff::
+	Copy the modified files to a temporary location and perform
+	a directory diff on them. This mode never prompts before
+	launching the diff tool.
+
 -y::
 --no-prompt::
 	Do not prompt before launching a diff tool.
@@ -30,11 +36,9 @@ OPTIONS
 
 -t <tool>::
 --tool=<tool>::
-	Use the diff tool specified by <tool>.
-	Valid diff tools are:
-	araxis, bc3, deltawalker, diffuse, emerge, ecmerge, gvimdiff,
-	kdiff3,	kompare, meld, opendiff, p4merge, tkdiff, vimdiff and
-	xxdiff.
+	Use the diff tool specified by <tool>.  Valid values include
+	emerge, kompare, meld, and vimdiff. Run `git difftool --tool-help`
+	for the list of valid <tool> settings.
 +
 If a diff tool is not specified, 'git difftool'
 will use the configuration variable `diff.tool`.  If the
@@ -62,6 +66,9 @@ of the diff post-image.  `$MERGED` is the name of the file which is
 being compared. `$BASE` is provided for compatibility
 with custom merge tool commands and has the same value as `$MERGED`.
 
+--tool-help::
+	Print a list of diff tools that may be used with `--tool`.
+
 -x <command>::
 --extcmd=<command>::
 	Specify a custom command for viewing diffs.

git-difftool--helper.sh

@@ -73,9 +73,16 @@ then
 	fi
 fi
 
-# Launch the merge tool on each path provided by 'git diff'
-while test $# -gt 6
-do
-	launch_merge_tool "$1" "$2" "$5"
-	shift 7
-done
+if test -n "$GIT_DIFFTOOL_DIRDIFF"
+then
+	LOCAL="$1"
+	REMOTE="$2"
+	run_merge_tool "$merge_tool" false
+else
+	# Launch the merge tool on each path provided by 'git diff'
+	while test $# -gt 6
+	do
+		launch_merge_tool "$1" "$2" "$5"
+		shift 7
+	done
+fi