Use the presence check for slab_nomerge.
Also check that slab_merge is not set.

Reusing "is not set" for CmdlineCheck is a nice hack.

Nice!

populate_with_data() must be called after all checks have been added.

Thanks to the coverage info

And also test the tool without "-l".

This is the feature for #46.

Thanks to @izh1979 for the idea (and for the rodata idea too).