Update ShrunkClient behavior on rejecting link
Update ShrunkClient behavior on rejecting link

Rather than returning False, it makes it more evident to the users of
ShrunkClient that something is wrong by throwing an exception.

See also: #41

ksuarz/shrunk,oss/shrunk,ksuarz/shrunk,ksuarz/shrunk,oss/shrunk,oss/shrunk,ksuarz/shrunk,oss/shrunk,oss/shrunk