[patch] deprecation warnings branch

[Jamie Wilkinson]

This one time, at band camp, Robert Collins wrote:
>@deprecated_function(zero_seven)
>def get_bzr_revision():
>    """If bzr is run from a branch, return (revno,revid) or None."""
>    import bzrlib.errors
>    ...
>
>results in the following pydoc output:
>Help on function decorated_function in bzrlib:
>
>bzrlib.get_bzr_revision = decorated_function(*args, **kwargs)
>    If bzr is run from a branch, return (revno,revid) or None.
>    
>    This function was deprecated in version 0.7.
>
>I'm not sure how to change the 'bzrlib.get_bzr_revision =
>decorated_function(*args, **kwargs)' line - that seems a little ugly to
>me right now.

FWIW this also affects the output of build-api, all decorated functions
appear without documentation and their signature as (self, *args, *kwargs),
which suck because after tracing the structure in the browser you have to go
open the file in an editor anyway :)  (Better go learn ctags I guess :)