recommendation: flood filter

I just accidentally double clicked while submitting an image comment and it posted the comment twice. Implementing some type of flood filter is strongly recommended to prevent people from running scripts to insert comments at a pace and amount which could potentially cause a break in the software, corruption of the database, or just a denial of service to other users.

Before a comment is accepted, you could do a simple check for:
- length of time between current and last comment (less than 2 or 3 seconds would indicate use of a script)
- whether the current comment is a duplicate of the last comment on the same item