To raise the max size for file uploads, it’s not enough to set upload_max_filesize to 50M.  One also has to set post_max_size to something that is at least as big.  I don’t think that’s how it used to be, or I wouldn’t have spent an hour looking for the solution.

I’m running Ubuntu now, so I put the extra settings in a separate file that I upload to /etc/php5/conf.d/ using chef.