rfc: remove "revision specs"

[Martin Pool]

Previous versions of bzr allowed for "revision specifiers" to occur
within a path, e.g.

  ./bzr.dev/@1040

User feedback has been fairly clear that people would prefer just to
use the -r options they're accustomed to from cvs and svn.  Not all
commands handle them.  So I propose to just delete support for
revision specifiers.

In previous versions it was necessary to use a revision specifier for
the merge command, but not anymore.

-- 
Martin