Test ConnectionPool#checkout
Test ConnectionPool#checkout with a thread
Test ConnectionPool#checkin
Alphabetize
Test ConnectionPool#checkout with timeout
Test ConnectionPool#checkin without connections

This would raise NoMethodError because the stack was never assigned.
This causes #checkin to become a no-op which may not be desired
behavior.
Test checkin after multiple checkouts

The local thread records how many times a connection has been checked
out so it can be returned to the pool when all have been checked in.
Test ConnectionPool#with

Ensure that a connection is checked out and checked back in properly.
Merge pull request #49 from drbrain/improve_connection_pool_tests

Improve connection pool tests