etags support now in ('make tags')

[Benjamin Kosnik]

It looks like automake has generic support for making tags, in that
'make tags' in the build directory is supposed to make a file TAGS
that one can then use in emacs, or whatever.

However, this was broken to do all the trickster string instantiation
fake-out files.

It's now fixed. The resulting TAGS file in in the top level of the
build directory. People who are interested, give it a whirl. I'm sure
more sophisticated TAGS files can be built, so patches to tweak this
(ie, something more than 'etags -C $(files)') are welcome.

-Benjamin