Add git-clean command

This command removes untracked files from the working tree.  This
implementation is based on cg-clean with some simplifications.  The
documentation is included.

[jc: with trivial documentation fix, noticed by Jakub Narebski]

Signed-off-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

git-clean.sh

@@ -0,0 +1,80 @@
+#!/bin/sh
+#
+# Copyright (c) 2005-2006 Pavel Roskin
+#
+
+USAGE="[-d] [-n] [-q] [-x | -X]"
+LONG_USAGE='Clean untracked files from the working directory
+	-d	remove directories as well
+	-n 	don'\''t remove anything, just show what would be done
+	-q	be quiet, only report errors
+	-x	remove ignored files as well
+	-X	remove only ignored files as well'
+SUBDIRECTORY_OK=Yes
+. git-sh-setup
+
+ignored=
+ignoredonly=
+cleandir=
+quiet=
+rmf="rm -f"
+rmrf="rm -rf"
+rm_refuse="echo Not removing"
+echo1="echo"
+
+while case "$#" in 0) break ;; esac
+do
+	case "$1" in
+	-d)
+		cleandir=1
+		;;
+	-n)
+		quiet=1
+		rmf="echo Would remove"
+		rmrf="echo Would remove"
+		rm_refuse="echo Would not remove"
+		echo1=":"
+		;;
+	-q)
+		quiet=1
+		;;
+	-x)
+		ignored=1
+		;;
+	-X)
+		ignoredonly=1
+		;;
+	*)
+		usage
+	esac
+	shift
+done
+
+case "$ignored,$ignoredonly" in
+	1,1) usage;;
+esac
+
+if [ -z "$ignored" ]; then
+	excl="--exclude-per-directory=.gitignore"
+	if [ -f "$GIT_DIR/info/exclude" ]; then
+		excl_info="--exclude-from=$GIT_DIR/info/exclude"
+	fi
+	if [ "$ignoredonly" ]; then
+		excl="$excl --ignored"
+	fi
+fi
+
+git-ls-files --others --directory $excl ${excl_info:+"$excl_info"} |
+while read -r file; do
+	if [ -d "$file" -a ! -L "$file" ]; then
+		if [ -z "$cleandir" ]; then
+			$rm_refuse "$file"
+			continue
+		fi
+		$echo1 "Removing $file"
+		$rmrf "$file"
+	else
+		$echo1 "Removing $file"
+		$rmf "$file"
+	fi
+done