Looks good to me.

Implemented #2. I personally think that's sufficient, because even if 
deleting comments, this shouldn't happen too often (mostly as a spam 
protection), so a comment number shift shouldn't hurt too much.

Recommend cross-linking using URI fragments:



Examples for how to access comment #242:

1. Direct access via a URL:

http://example.com/horde/whups/ticket/?id=142&Horde=MD5HORDEID#242



2. Comment text like this: "Issue 431#242" gets turned into URL like above.
Yep:



CREATE TABLE whups_comment_sequences {

      ticket_id INTEGER NOT NULL,

      next_comment_number INTEGER NOT NULL

}

Probably useful for things like comment feeds and for making nicer 
interfaces involving links to tickets. Wouldn't be hard to do if we 
created a sequence for each ticket, but that'd be a _lot_ of 
sequences. Probably easier to have a table of sequences with two 
columns: ticket_id and comment_sequence.

It would be helpful to number comments for easier reference,   
especially in the following scenarios:

1. Discussing a ticket over the phone while both parties are looking 
at the ticket online

2. Responding to multiple comments in a single comment block



I see at least two ways to do this:

1. Simply use the value from whups_comments.comment_id

+ Easy to implement

- Not guaranteed to be sequential

2. When rendering, number the comments with oldest = 1

+ Easy to implement

- Comment #s may be inaccurate if comment is deleted

3. Uniquely number comments within a ticket

+ Resilient to deletions of comments

- More difficult to implement



I personally wouldn't mind #1, but I know that will confuse many, if 
not most, users.  I don't immediately recall anyway to delete comments 
from the UI (perhaps that should be another ticket?), so #2 would work 
fine except for when deleted out from under whups in the db directly.   
#3 is probably the best way to go.