req: bump threads only when author ask a bump

this is not complicated, i'm sure, but i'm stupid...

basically, the forumdisplay shows the threads in "Creation Date" listing, and the threads are bumped to the top only when the author of the thread click to bump it...

reason: good for something like the "I updated my first post" thing... can be used about in any situation, from recipes to product reviews to hacks releases...

so the threads are listed by production date, and by modification date of the first post (or last time the author post in the thread)...

it's a mix of many features, i think i can't handle it (too humble to do all the job)