Increase the maximum allowed jpeg filesize.

I was able to get real close to the current limit without trying too
hard (within 1K), so this seems a bit too low. Bumping it up by 50%
still keeps it fairly low and has little effect on anything, but keeps
us safer from discarding legitimate posts.

Fixes #71.
Merge pull request #73 from meatspaces/filesize_increase

Increase the maximum allowed jpeg filesize.