Fix hiding the 'say' bubble WRT number formatting

When setting bubble text, numbers are rounded to two decimal places if
necessary. The check before hiding the bubble that makes sure the
current bubble text matches the current value -- probably intended to
make sure it's "our" bubble -- now uses the same text formatting code to
avoid false negatives.
Hmm... I could see it going either way. I set the source so that you can always trust that it would be set to a meaningful value; it's possible that we might want to check it in the future for some reason, or the value might be helpful in debugging.
Can you think of a reason it would be harmful or misleading to set the source like this? My understanding of the current code is that the value set in this case won't be used, but also won't hurt anything.