Adjust regex to match without trailing "//"

[kennonb]

This might break things I'm unaware of so feel free to decline this. 😊 I noticed that while moving Mail messages into OF it creates URLs like:

message:%IDENTIFIER%3E

The problem is that the current regex requires there to be a trailing // in that URL:

message://%IDENTIFIER%3E

I could just add those, but when I'm dragging 4-5 emails into OF, it becomes a chore to go through each one and modify.

Also I found that my modification then would match on times like 08:00:00, so I made another change so that : can't have a digit directly after it. I don't know of any URLs that do this, but that could cause some unforeseen issue.

To sum up:

• I wrapped \/{2,3} in a conditional so that // doesn't have to exist in the URL
• I added a negative lookahead so that the : cannot have a space or a digit directly after it
• I also added @ to the approved characters as Mail likes to append the account type at the end @gmail for instance

[ksalzke]

Thanks @kennonb - seems like a useful change to me; I'll go ahead and accept it!