fix row chart labels so they are vertically aligned *always*
artifacts
test vertical positioning of row labels

this was an attempt to test #732, but the existing data is not big enough
to test this properly

still, i think it's a good idea, so i'm committing it
Merge branch 'merge-732'
reverse and rename flag for whether labelOffsetY is set

somewhat clearer to set a flag when property is set?
anyway, i thought "default" was unclear
revise test for Y positioning of row chart labels

proper test for #732
it actually was properly failing even with just 7 rows
revise it to check centeredness instead of withinness