(TK-23) Update to clj-http-client 0.2.1

This commit updates jetty9 to the latest clj-http-client release,
and in the process, fixes some transient test failures having
to do with a race condition.  (SSL-related tests that were intended
to cause exceptions could end up with one of two different exceptions
when we use an asynchronous HTTP client.)

Conflicts:
	test/clj/puppetlabs/trapperkeeper/services/webserver/jetty9_service_proxy_test.clj
(TK-23) Get rid of unnecessary calls to `true?`
Merge pull request #48 from cprice404/bug/master/TK-23-update-to-http-client-0.2

(TK-23) Update to clj-http-client 0.2.0
Update CHANGELOG for 0.6.1 release
Merge pull request #51 from cprice404/maint/master/CHANGELOG-for-0.6.1

Update CHANGELOG for 0.6.1 release
lein-release plugin: preparing 0.6.1 release
lein-release plugin: bumped version from 0.6.1 to 0.6.2-SNAPSHOT for next development cycle
(TK-50) Require user to specify default server

Require user to specify a default server when using a multiserver
configuration. Update docs and example to reflect this change.
(TK-50) Change default server configuration

Change the configuration of a default server to be a boolean
contained in the map for one server in a multiserver set-up.
Make the default server specification optional.