Merge pull request #594 from ddotlic/master

Fixed SL5 compilation
Add useful AssertDir Ext
INCR to v3.9.44
Enable specification of external assemblies for controller discovery on ServiceStack.Mvc.FunqControllerFactory.  Unit tests added to preserve default behaviour in:

tests\ServiceStack.Mvc.Tests\
tests\ServiceStack.Mvc.Stubs.Tests\
Add ValidationError.ErrorResponseFilter customization hook to return custom errors
Allow EndpointHost.GetPlugin<T> to return null for unregistered plugins
Doesn't need the pluginsLoaded check
Setting inner asyncClient cookie from ServiceClientBase

Setting the async client cookie container when the container is replaced
on the base service client.
Move ServiceStack.Mvc.Stubs.Tests to external lib test assembly
Remove ServiceStack.Mvc.Stubs.Tests project from ServiceStack.sln
Merge pull request #600 from chappoo/master

Enable specification of external assemblies for controller discovery …
Merge pull request #601 from AdamCLarsen/master

Fixes #116 CookieContainer of the inner asyncClient field in ServiceClientBase is not updated
Set a new expiration date when adding a permanent cookie.

Ultimately want to help ensure uniqueness of cookie name and expiration.
Merge pull request #604 from jeffgabhart/permanent-cookie-exp

Get a new expiration date when adding a permanent cookie.
New SL5 binaries for 3.9.44.

To be used with the next NuGet package.