Restore email attachment functionality

[orangejulius]

In #111, we were forced to temporarily disable sending of our response details attachment with our acceptance test emails. Apparently Amazon SQS has a strict 10MB limit and we were hitting that.

In the long run, this attachment is really useful. It lets us see the full debug output for queries that didn't work, which may help track down configuration issues and is especially helpful with transient errors.

However, we need to ensure the size is manageable for a long time (since we of course always want to add more acceptance tests).

Some ideas to manage this include:

• Compressing the output and setting proper headers so that email clients handle it transparently
• Pruning the debug output where there is non-essential information
• Only returning debug output for test cases that failed