Merge branch 'jc/diff'

* jc/diff:
Libified diff-index: backward compatibility fix.
Libify diff-index.
Libify diff-files.

diff --combined Makefile
index 809383c51b6512d9c33773ba9d35278b8d1ccdf4,0924f84c4f8b964b18e97670ad8d407f99f08ecf..087ff27c28960a552e3a97126ada4f64ca391844
--- 1/Makefile
--- 2/Makefile
+++ b/Makefile
@@@ -199,7 -199,7 +199,7 @@@ LIB_H = 
        tree-walk.h log-tree.h
  
  DIFF_OBJS = \
-       diff-lib.o diffcore-break.o diffcore-order.o \
+       diff.o diff-lib.o diffcore-break.o diffcore-order.o \
        diffcore-pickaxe.o diffcore-rename.o tree-diff.o combine-diff.o \
        diffcore-delta.o log-tree.o
  
@@@ -575,7 -575,7 +575,7 @@@ $(patsubst git-%$X,%.o,$(PROGRAMS)): $(
  $(DIFF_OBJS): diffcore.h
  
  $(LIB_FILE): $(LIB_OBJS)
 -      $(AR) rcs $@ $(LIB_OBJS)
 +      rm -f $@ && $(AR) rcs $@ $(LIB_OBJS)
  
  XDIFF_OBJS=xdiff/xdiffi.o xdiff/xprepare.o xdiff/xutils.o xdiff/xemit.o