[vm] New summary faces integration

[Tim Cross]

I just looked at the work Uday has completed to bring vm-summary-faces.el into
VM core. There is a change I would like to suggest (which I'm happy to
implement) which I think would further improve things. 

The package has a number of face definitions along the lines of 

(defface vm-summary-marked-face
  '((((type x)) (:foreground "red3")))
  "The face used in VM Summary buffers for marked messages."
  :group 'vm-summary-faces)

(defface vm-summary-deleted-face
     (if (featurep 'xemacs)
         '((t (:foreground "grey50" :strikethru t)))
       '((t (:foreground "grey50" :strike-through "grey70"))))
     "The face used in VM Summary buffers for deleted messages."
     :group 'vm-summary-faces)

(defface vm-summary-new-face
  '((t (:foreground "blue")))
  "The face used in VM Summary buffers for new messages."
  :group 'vm-summary-faces)

What I would like to suggest is that instead of directly setting the face
properties, we use the :inherit tag and use 'standard' faces for the defaults.
The reason I think this is a better idea is

1. The 'standard' faces have been defined so that they provide reasonable
defaults regardless of environment i.e. X, console, etc.

2. Those users who like to customize their faces will probably already have
done so for the standard faces. Having VM inherit from those settings means
they will probably get better default results.

3. For users who use the colour-themes package, the default VM faces will
likely fit in with their colour theme better if they are inheriting from
standard faces. 

4. We don't need to worry about personal taste and our selected defaults. If
people don't like the defaults, they can take the issue up with the emacs
maintainers. 

5. We don't need to worry about setting defaults that take into account those
who use light backgrounds and those who use dark ones etc.

Comments, opinions?

Tim