Added IsProperty() check to result in DefineOrRedefineAccessor - if no check

Added IsProperty() check to result in DefineOrRedefineAccessor - if no check
this causes the debug check to fails since type() asserts that the
lookup_type != NOT_FOUND. This does not change any functionality since we
explicitly checked if it was one of the three types that we need to delete.
Also changed defineProperties in v8natives to actually return the object
being defined (as specified by spec)

Review URL: http://codereview.chromium.org/572003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3794 ce2b1a6d-e550-0410-aec6-3dcde31c8c00