RFA: implement ambiguous linespec proposal

[Tom Tromey]

Jan> Still more time could give more reviews, for whatever reason I for
Jan> example haven't yet run a regression test on `break'ing on all
Jan> symbols of Fedora .debug files which found regressions in Keith's
Jan> patchset, also I haven't yet found energy for the full review for
Jan> whatever reason.

Tom> I'll try this test against the debuginfo I have installed here.

I ran it against a big C++ library, libwebkitgtk.  This took long enough
that I don't think I want to run it against everything.

This revealed one pre-existing bug, but nothing specific to my patch:

    http://sourceware.org/bugzilla/show_bug.cgi?id=13417

Tom