add clean and ignore rules for xdiff/

Signed-off-by: Junio C Hamano <junkio@cox.net>

.gitignore

@@ -128,8 +128,7 @@ common-cmds.h
 *.deb
 git-core.spec
 *.exe
-libgit.a
-*.o
+*.[ao]
 *.py[co]
 config.mak
 git-blame

Makefile

@@ -629,7 +629,8 @@ rpm: dist
 ### Cleaning rules
 
 clean:
-	rm -f *.o mozilla-sha1/*.o arm/*.o ppc/*.o compat/*.o $(LIB_FILE)
+	rm -f *.o mozilla-sha1/*.o arm/*.o ppc/*.o compat/*.o xdiff/*.o \
+		$(LIB_FILE) $(XDIFF_LIB)
 	rm -f $(ALL_PROGRAMS) git$X
 	rm -f *.spec *.pyc *.pyo */*.pyc */*.pyo common-cmds.h TAGS tags
 	rm -rf $(GIT_TARNAME)