2.13.50 won't build

[Graham Percival]

While building 2.13.50, the doc build failed as usual, but I restarted
it and it seemed to complete successfully.  I went ahead with the
release because I thought it was the normal failure from a few days
ago, but I didn't check the actual cause because I wasn't really
paying attention.

Independent of that, I did a doc build from scratch, and discovered
that git won't build; presumably the same issue I saw in the release.


In the context of a full doc build from scratch, the following example
from Learning fails:
<<
  \relative c' {
    \key g \major
    \time 3/4
    \partial 4
    d4 | g4 g a8( b) | g4 g b8( c) |
    d4 d e | c2
  }
  \addlyrics {
    A -- | way in a __ | man -- ger,
    no __ | crib for a | bed, __
  }
>>
I don't see that behaviour when compiling it from scratch.


Just a warning for anybody who can't figure out why they can't build
the docs in git when I apparently could.

Cheers,
- Graham