* Add plugin IPC and discovery
* Update timeout defaults to match spec
* Use PluginUtilities in functional test
* Fix tests for other platforms
* Fix NuGet.Protocol functional tests on non-Windows platforms
* Fix and add functional tests
* Add tests
* Apply review feedback and minor fixes
* Fix test and improve fast path for plugin discovery
* Fix unit test failure
* Remove unused field
* Apply verbal review feedback
* Improve MessageDispatcher tests
* Fix MessageDispatcher tests
* Fix ConnectionOptions test
* Fix ConcurrentDictionary<T,U>.GetOrAdd(...) calls
* Simplify UTF8 handling
* Fix test name
* Enable plugin package download
* Fix issue where a plugin was not queried for operation claims for each package source
* Fix plugin package download in dotnet.exe.
* Fix plugin package install, get credentials in multifeed environment, and add get service index request/response.
* Change AutomaticProgressReporter to accept a connection
* Apply review feedback.