Fixing ActorPath impl, reducing memory footprint.
RootActorPath does no longer keep a name field
update FsPickler version
Reverting RootActorPath changes
cached elements evaluation in ResolveActorRef
Be able to create prerelease packages and publish to custom feeds

New build parameters:
- nugetpublishurl: The feed to publish too. Uses default if not specified
- nugetprerelease: Prerelease prefix.

Example: If "-nugetprerelease=dev" is used as parameter when executing
build.cmd a prerelease package will be created with a version on the format:
version + "-dev" + DateTime.UtcNow (unfortunately seconds had to be left
   out as Fake only supports an int)
For example: 1.6.4-dev14081911
Run MStest on Akka.TestKit.VsTest.Tests.dll
Add test that recreates bug #293

ReceiveActor never receives any messages if Base.OnPreStart isn't called from PreStart override
ReceiveActor should be initialized from ActorCell instead of doing it itself.

Fixes bug #293.
If the user did not call base.PreStart() or base.PreRestart(), Init() was never called
This introduces a new interface InitializableActor, wich has an Init method that is
called by ActorCell instead.