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>

Documentation/git-write-tree.txt

@@ -20,7 +20,7 @@ The cache must be merged.
 Conceptually, "git-write-tree" sync()s the current directory cache contents
 into a set of tree files.
 In order to have that match what is actually in your directory right
-now, you need to have done a "git-update-cache" phase before you did the
+now, you need to have done a "git-update-index" phase before you did the
 "git-write-tree".
 
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