更好的tag和cscope的支持

从log上看都加了差不多快半年了，把 make tags 和 make cscope 的工作从原来的 Makefile 里面分离出来了，引用 commit 如下：

commit a680eedc6c621c75695c68198533fc3c98f4053b
Author: Sam Ravnborg
Date:   Wed Dec 3 22:24:13 2008 +0100

    tags and cscope support really belongs in a shell script
    as they do not benefit from the make functionality.
   
    Moving the support to a shell script has several benefits:
    - The readability of the code has increased a lot
    - More people is able to extend the tags support
    - We see less changes to the top-level Makefile
   
    The shell script version includes improvements from:
    Alexey Dobriyan (jump to kconfig symbols)
    Alexey Dobriyan (drop ./ in paths)
    Ian Campbell (simplified find algorithms)
   
    This version has a few caveats:
    => It does not support ALLSOURCE_ARCHS
       - it is easy to add if it is really used
    => It assumes all archs have moved to arch/$ARCH/include
       - until that happens we have a few additional hits in the archs
   
    Signed-off-by: Sam Ravnborg
    Cc: Alexey Dobriyan
    Tested-by: Ian Campbell

实际使用起来，生成 tags 等的命令还是一样的，和原来没有差别，但是生成的 tag 和 cscope.out 就不一样了，从体验上来说，比原来好用的多了。

嗯。体验提升了，一定要赞。

此外，一直不晓得的用法也要备份一下：

$gvim -t just_for_fun

Hope that you won't go straight forward with above command.

:---)