Changed Count property in ProcessingQueue to include in-flight items.
When dequeing an item from a ProcessingQueue, we need to adjust the capacity as well.
Use a processing queue for HttpTransport to ensure that we don't exceed a set limit of concurrent requests.
Improved comments for how _capacity is computed in ProcessingQueue<T> and also spotted an issue with TryDequeue() (not yet fixed).
Applied code-review changes to HttpTransport.
Added 'readonly' modified to static field.
(BREAKING CHANGE) Fixed ProcessingQueue<T>.TryDequeue().  This required a change to the implementation that now makes it impossible to support unlimited fanout.  However, this is not an issue since unlimited fanout can be done by just submitting to the dispatch queue directly.
Merge branch '2.5' into DR-116
Merge remote-tracking branch 'origin/DR-116' into DR-116
HttpTransport: reverted changes (except for resharper clean-up) to match the 2.5 implementation
HttpTransport: un-resharpered file to minimize changes from original
DreamHostService: use a ProcessingQueue to manage the number of requests we can process concurrently
DreamHostService: only create ProcessingQueue for inbound requests when connection limit is positive
DreamTestHelper: added optional argument to initialize the connection limit
DreamHostTest: removed test that checked what happened when connection limit was exceeded
Merge branch '2.5' into DR-116
HttpTransport: use 'this.' prefix when initializing fields/properties
DreamHostService: dismiss pending requests when shutdown is initiated
Merge branch '2.5' into DR-116
Merge pull request #104 from bjorg/DR-116

DR-116 Implement a request queue so limit max parallel requests