LilyPond 2.13.17 released

[Graham Percival]

We are happy to announce the release of LilyPond 2.13.17. This
release includes bugfixes for 4 critical issues. However, 15
critical issues still remain, so this release is intended for
developers only.

To clarify any lingering confusion: the announcement of 2.14.0
(including known regressions bugs) on April 1st was a prank.  We
will not release 2.14.0 if we know of anything which worked in
2.12 or 2.10 but does not in the 2.14 candidate.

Cheers,
- Graham