Please make etags path-aware

[Matzi Kratzi]

I maintain multiple versions of the same SW and I have always multiple
revisions from different branches of the same files loaded
simultaneously in the same emacs.

etags is wonderful, but I have to remember to visit-tags-table every
time my focus switches. Couldn't emacs do this for me?

All my sw are located like this
k:\src\Produkt1_release1
k:\src\Produkt1_release2
k:\src\Produkt1_release3
k:\src\Prudukt2_release1

It would be nice if you somehow could connect a src-path to a tags-path:

c:\tags\Produkt1_release1\TAGS
c:\tags\Produkt1_release2\TAGS
c:\tags\Produkt1_release3\TAGS
c:\tags\Prudukt2_release1\TAGS

"k:\src" could then be a variable as well as "c:\tags". Some would
probably choose to use the same value for these to variables.

Anyhow; tags-verify-table checks that the table has not been updated
since loading it. Couldn't that function be made to check for a
logically "better" TAGS?