vc-annotate uses git blame's "-M" to detect moved/copied lines within a file

It already used "-C -C" to detect lines moved or copied from other files
that were modified in the same commit (the first "-C") and the commit
that creates the file (the second "-C"). If you give a third "-C" it
looks for copies from other files in any commit, but presumably that
will be really slow. Before I enable that I'll need to find some plugin
to display the annotate buffer incrementally (with each line showing the
most coarse "last changed" commit until more accurate information is
known).
Fix pylint checkers' predicates

The predicate defines which buffers to enable a particular checker in.
The predicate is supposed to be a function that can be called from each
buffer. Without this change, it seemed to be *always* the
`stb-tester-checker' checker that was enabled for python code.