xref-find-matches and stuff

[Dmitry Gutov]

Hi all,

I've been considering a set of minor changes:

- Use lisp/cedet/pulse.el to briefly highlight the current line after 
the jump.

- Add the xref-find-matches command (as well as a corresponding backend 
action), for project-wide string searches (hopefully with regexp 
support). That probably doesn't sound as exciting as the existing 
commands, but it will be "Grep in a new UI", and it will eliminate the 
"select the directory" step.

- Further, using the same data we could implement "search and replace", 
in the same way as xref-find-references can get us to "rename".

- With this, xref-find-function starts becoming pretty fat. The 
"references" and "matches" actions can be split into a new variable 
(xref-scan-function?).

The current find-references implementation, as well as the anticipated 
find-matches one, are language-agnostic, so we can expect this variable 
to often keep its default value, especially if the default 
implementations use some kind of "current project" facility. So far, 
both etags and elisp backend's references implementations only differ in 
the directories lists they use.

Thanks,
Dmitry.