Issue 3625: Overrides via \tweak don't insist on proper context/grob and property split

The normal \tweak syntax of overrides is
\tweak property #value Context.Grob

This version just concatenates the symbol list at the end with the one
at the start before checking for a valid (possibly sub-)property path.
This allows a somewhat more flexible programmatic use.
Issue 3624: make-connected-path-stencil broke on closed paths

Cf. <URL:http://lists.gnu.org/archive/html/bug-lilypond/2013-10/msg00083.html>.
Actually, the whole function is an obfuscated Scheme programming
contest.  I made a few of the more flamboyant list manipulations
boring while at it.
Issue 3623: lilypond-book fails with file names containing shell-special characters
Issue 3616: convertrules override/tweak/revert transparent/stencil -> hide/omit/undo
Run scripts/auxiliar/update-with-convert-ly.sh

Actually, this is an understatement.  This is the result of

scripts/auxiliar/update-with-convert-ly.sh
git checkout HEAD ly/{engraver,music-functions,property}-init.ly input/regression/display-lily-tests.ly Documentation/{,*/}learning/*.itely

and then committing.
Revert "Issue 3616: convertrules override/tweak/revert transparent/stencil -> hide/omit/undo"

This reverts commit 7c0b941c3854a47f84e71827b761b0ae88d13803.
Some slight Documentation changes for \hide/\omit
Issue 2392: Segfault in connection with \applyContext
Improve formatting of PaperColumn debug info

Paper_column::print can be very helpful in debugging spacing
information, but until now its output was not very readable.
This patch:
 - decreases font-size of debugging info so that it doesn't
   collide and overlap everywhere,
 - makes it possible to override the size of the arrow values
   with font-size property,
 - makes both red and blue arrows point in the same direction
   (previous situation was confusing)
 - centers the spring and rod values on the arrows (previously
   it was hard to discern which number goes to which arrow),
 - prints debugging info always on top,
 - makes arrows and the distance between them scale with fontsize.
Small correction to Issue2392
Issue 3458: Document \alterBroken