Add a test case for #1267: block append in include is ignored when the block is not referenced in the including .jade
Add a test case for #1267: block append in layout without extending is ignored.

The append action is not visible in the result, but the block append is not totally ignored as it yields the current value of the block.
Add another test case: when redefining a block inside another block it's currently ignored.

It works when the block is not already redefined in the extending block, see layout.block.replace-block-in-other-block-without-prior-block.jade (except for the unexpected yielding).
Another test case: block redefinition and previous append.