Better parser for code blocks.

* A line containing a comment with no identation will now end a code
  block.
* Code blocks no longer need to be followed by a blank line.

[SVN r64829]

tools/quickbook

@@ -1 +1 @@
-Subproject commit 7101c28eba505dcd9fe21d89c844b322e566fc66
+Subproject commit e6416985367537c50b5f376972fbaf5734ba11df