* M9: name a laid-out XFA form's signature fields by their SOM path, so other viewers find the signature
* M9: doc comments on the functions the signature naming touches
* M9: say other viewers in the signature naming's comments
* M9: a new layout keeps a signature a generated signature box holds
* M9: the re-layout test checks the signature's picture is kept too
* M9: a signature field named by its SOM path doesn't repeat a name a field already has
* M9: every name a field of the pass takes is known before a signature field is named, in either order
* M9: the signed-box test's doc comment is back on its test
A merge had left it above the next test, which has its own.