according to the RFC (2396), URIs can't have '_' in the scheme.
recent changes to mozilla/netwerk enforced this rule, which caused bug
#110502 ("fwd inline" and "edit as new" failed to bring up a compose
window.)
Previously, our URI schemes for messages were: mailbox_message,
news_message, imap_message
now, they are: mailbox-message, news-message, imap-message
If you get alerts like: "mailbox-message is not a registered protocol",
you need to update and rebuild mozilla/mailnews. you might need to
clobber as well.
On a related note, one day we might switch to "moz-mailbox-message", as
these are internal URIs to mozilla.
-Seth
