Tests:
A scenario I thought of based on my experiences with this bug: <rdar://problem/4045521> Hitting return key with full line selected does not add blank line as it should
Expected Results:
Should see this content in the red box below (note that there should be two blank lines between "foo" and "baz"; also note that the insertion point should be at the start of the third line, a blank line):
foo
baz
foo
bar
baz