Make debug mode more useful

In relation to the patch for #1793272: Switch from cURL to drupal_http_request for HTTP requests, and the proposal to remove the debug code in it, I'd like to propose instead of removing it, it would be good to make it more useful.

We have a two distinct problem-spaces that could be part of the same configuration option. 1. My block doesn't work, and I don't know why (the reason for #1497288: Add a debug mode and 2. I'm working on my theme and I need to cache more aggressively so I don't hit my twitter limit, which we've been discussing in #1514738: Tweet caching may be too agressive.

I can't think of overlap between the two issues, so it would be a simple radio button/select for modes, 1. normal, 2. cached, and 3) debug. Cached would cache aggressively, and Debug would log the entire twitter response to watchdog.

While we are here, I'd also like to consider a way on the edit page to see (and possibly manually edit, but I'm iffy on edit) the request which will be used with current configuration options. Something folks could copy and paste into an issue which might help us identify problems. Editing might allow advanced users to create more complex requests, but again I'm a little concerned about the can of worms that might open up.

I do have a couple of higher priority items on my plate right now, but I wanted to get this into the queue so we can at least discuss it, and as always, I gladly accept patches.