Add hook_token_values_alter() to allow altering of tokens

Currently, there's no way for one module to alter the list of tokens defined by another module.

For example, if module_a defines a token like "username-url" whose value is a link to the user page with the link text "Click Here For My User Page", there is no way for module_b to replace that link text with, for example, values from the user's profile.

This patch adds a drupal_alter() call to token_get_values() so that other modules can intercept and adjust already-defined values as necessary.
D7 already handles this in token_info() and token_generate() using drupal_alter(), but the same functionality was never backported.

Is there a better way to do this in D6 that I'm overlooking?

I haven't followed the discussion on this, and a quick search on the queue didn't turn up much, so please forgive me if i'm re-treading old ground.