Further robustness improvements

- Sometimes key is partially truncated (like key=Reference>. Handle this gracefully
- When running tests we don't have "SERVER_SOFTWARE" in the environment. Handle it gracefully
- Sometimes the query string comes back as unicode (even though it doesn't contain unicode chars ???), but headers only support ascii
- Don't add truncation markers ('...') to the structures (list / dicts) to avoid confusing code in cleanup
Keep appstats enabled

This commit adds the option for the user to tell gae_mini_profiler: "keep appstats enabled, even if the configuration says that profiling should be disabled". Ie. decouple the disabling of appstats from the disabling of gae_mini_profiler.

For a discussion why this is needed, please see https://github.com/kamens/gae_mini_profiler/pull/46#issuecomment-14624342
Merge branch 'keep_appstats_enabled'