TALES namespace names cannot contain '-'

Hi,

I recently wanted to make a TALES namespace called 'enum-value' for use
in Launchpad development.

I found that this didn't work, because only the characters [a-zA-Z0-9_]
are allowed.  You can find the regex on line 27 of
zope/tales/expressions.py.

  namespace_re = re.compile('(\w+):(.+)')


I propose to extend this to allow the '-' character too.

Any objections to this?

Are there any other characters that should be included?

Do any specifications need changing?

-- 
Steve Alexander