ctags: usability fix

The tag file generated by the tags.sh script has some issue.

First:
  The identifier-list miss the
  DEFINE_TRACE,EXPORT_TRACEPOINT_SYMBOL,EXPORT_TRACEPOINT_SYMBOL_GPL
  special handling, which can result in a wrong tag, not to jump to the
  right variable definition or function implementation.

Second:
  It makes no real sense to include function prototypes and external and
  forward variable declarations, because jumping to a tag will sometimes
  go to this and not to the real definition and implementation. The information
  about the declaration is still there at the definition and implementation
  place.

So this patch make it lot easier to navigate through the kernel source
tree using vi.

Signed-off-by: Stefani Seibold <stefani@seibold.net>
Acked-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>