provide a default value for local host name lookups
Merge pull request #304 from pyr/issue-233

provide a default value for local host name lookups
Threadpool executor service: better queue depth estimate.

Now ignores tasks actively executing.
Merge branch 'master' of github.com:aphyr/riemann
Adjust threadpoolservice queue/pool parameters.

Experimentation with async-queue suggests these will better meet the
default needs of users for IO-bound pools.
Do not assume numbers for comparisons in top.

This allows hierarchical sorting, useful to determine trends.

For instance:

```clojure
(top 10 (juxt :metric :time)
     (tag "spiking" index)
     index)
```
Correct switch to compare instead of number assumptions.
Provide a demotion stream for events bumped out of the top-k.
Merge pull request #306 from pyr/feature-top-expire

Do not assume numbers for comparisons in top.
better fix for aphyr/riemann#233
Indexing an expired event should result in removal
Merge branch 'master' into feature-top-expire
Merge pull request #308 from pyr/feature-top-expire

indexing an expired event should result in removal
Merge branch 'issue-233' of github.com:pyr/riemann into pyr-issue-233

Conflicts:
	src/riemann/common.clj
Merge branch 'master' of github.com:aphyr/riemann
riemann.common/get-hostname: Docstrings, extract constant.