comark/include/open-block-in-partial

A partial that opens a :: block and never closes it would take in the rest of the page, so comark-include closes it at the end of the paste and reports it. Close the block in the partial instead of relying on that. Here tour.md opens ::carousel without its closing ::, and tour-closed.md has it.

:include{src="tour.md"}

:include{src="tour-closed.md"}