Link to explanation of --checksum-full rule.

Mark McLouglin made a _great_ post to a bug explaining why this rule is
needed.  Save off a link to it in the code.

Change-Id: I478b2f8de59f26d56385525a195108045507969c
Avoiding multiple code loops in filter scheduler

The code snippet can not provide the original target. In the
filters module, there is one line code will never be invoked
because of the code logic, so I modified it.

Fixes: bug 1186945
Change-Id: I3f2a662c28ab466b178268cae3502c40a1d22657
Merge "Avoiding multiple code loops in filter scheduler"
Merge "Link to explanation of --checksum-full rule."