parttagline in 2.13.x

[Nick Payne]

I have just installed 2.13.2 as an update to 2.12.2, and in one of my scores
that uses bookpart and parttagline, the parttagline for the bookpart does
not appear in the PDF unless I change its name from parttagline to tagline.
I get no errors shown in the console log either way. I haven't been able to
get a minimal example to show the same problem, and strangely, other scores
I have that use bookpart and parttagline continue to show the tagline
without needing the same change. With 2.12.2, parttagline works fine in both
scores.

I couldn't find any mention of parttagline in the 2.13 documentation except
in a couple of snippets.

I haven't tried to attach the score because I think it will exceed the size
limit for the mailing list. 

Nick