lily/parser.yy: whitespace fixes
Issue 3892/1: Allow output defs as scheme expressions in toplevel, book, bookpart.
Issue 3892/2: Allow scheme expressions for scores, output defs, music in scores
Count MIDI ticks from the beginning of the score, not each staff independently.

This keeps MIDI output aligned for:
* Lyrics (issue 3878)
* Staves without Dynamic_performer (issue 3871)
* Staves that start late
* Scores that start with grace notes (issue 1412).
More readable \displayMusic output. (issue 3893)

* Omit unnecessary optional arguments.
* Use rationals when printing moments (but not with grace parts, because that's ambiguous).
Fix infinite loop in Completion_heads_engraver at invalid measure position (issue 3888).

* Completion_heads_engraver now gives a programming_error instead of trying to make negative-duration notes.
* intlog2 with a nonpositive argument now gives an error instead of an infinite loop.
\partial now only makes measurePosition negative at the beginning of a score.

This is more consistent, and means it doesn't disrupt bar numbers when used
at the beginning of a measure or after \time. (issue 3888)

This changes the semantics for issue 3645 in commit
2d34420eaf1ffdb620739e4640af42c0b3f812c1.
Warn when \time is used in mid-measure, and reset measurePosition.

This makes issues 3696 and 3888 less mysterious.
Bad positioning of tuplet numbers on kneed beams with Beam.positions override.

Previously, when Beam.positions was overridden, tuplet numbers on kneed beams
would automatically be placed according to the bracket instead of against
the beam.  This happened because the check for whether the beam was kneed
or not returned false in such cases.  This patch replaces that check.

It also:

--adds a regtest demonstrating behavior with Beam.position overrides
--removes some redundant code
Revert "Restrict lilypond-book mingw32 subprocess workaround to Python versions < 2.6"

This reverts commit 1f2bdee043a85ddca79be8ef99b206fb3a97b289.
Issue 3874: lilypond-book: Fix TEXINPUTS environment manipulation on W32

This transfers the TEXINPUTS manipulation into the mingw32 workaround
where it was not previously being done.
Release: bump VERSION_DEVEL.
PO: update template.
Release: update news.
Release: bump VERSION.