Big tool rename.

As promised, this is the "big tool rename" patch.  The primary differences
since 0.99.6 are:

  (1) git-*-script are no more.  The commands installed do not
      have any such suffix so users do not have to remember if
      something is implemented as a shell script or not.

  (2) Many command names with 'cache' in them are renamed with
      'index' if that is what they mean.

There are backward compatibility symblic links so that you and
Porcelains can keep using the old names, but the backward
compatibility support  is expected to be removed in the near
future.

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

t/t4001-diff-rename.sh

@@ -27,7 +27,7 @@ Line 15
 
 test_expect_success \
     'update-cache --add a file.' \
-    'git-update-cache --add path0'
+    'git-update-index --add path0'
 
 test_expect_success \
     'write that tree.' \
@@ -37,11 +37,11 @@ sed -e 's/line/Line/' <path0 >path1
 rm -f path0
 test_expect_success \
     'renamed and edited the file.' \
-    'git-update-cache --add --remove path0 path1'
+    'git-update-index --add --remove path0 path1'
 
 test_expect_success \
-    'git-diff-cache -p -M after rename and editing.' \
-    'git-diff-cache -p -M $tree >current'
+    'git-diff-index -p -M after rename and editing.' \
+    'git-diff-index -p -M $tree >current'
 cat >expected <<\EOF
 diff --git a/path0 b/path1
 rename from path0