Mock->shouldAllowMockingMethod() returns $this instead of null
add shouldAllowMockingProtectedMethods() to MockInterface
change
  @return $this
to
  @return Mock
in PHPDoc Statement
add test for Mock::ShouldAllowMockingProtectedMethods()
Merge pull request #333 from fhinkel/master

Mock->shouldAllowMockingMethod() returns $this instead of null