(SERVER-204) Subcommands for 'ruby' and 'irb'

Working implementations for ruby and irb to go along with the gem
subcommand. Acceptance tests need to be written, as well as docs.
(SERVER-204) Set compatibility version and improve load path order
(SERVER-245) Avoid Puppet 4 being used as a dependency

Without this patch puppet-server allows any version of Puppet >= 3.7.3.
This is a problem because Puppet 4 is on the horizon and will introduce
changes in behavior incompatible with behaviors we depend on.

This patch addresses the problem by specifying that RedHat and Debian style
packages should only use puppet packages >= 3.7.3 and < 4.0.0 to satisfy
the dependencies for puppet-server.
(SERVER-151) Add jruby-pool HTTP Admin endpoint

Add a jruby-pool endpoint to the HTTP Admin API that, when given
a DELETE request, will flush the JRuby pool.
(SERVER-151) Address PR feedback

Add comment to jruby-pool-resource similar to that for the
environment-cache-resource. Change resources test directory for
jruby-pool-int-test. Remove unnecessary Accept header from
test of the jruby pool endpoint. Add tests to ensure that the
jruby-pool endpoint tolerates an 'Accept: */*' header and that
it denies access when a cert is not on the whitelist.
(MAINT) Update changelog