[patch] Print all headers in \book

[Graham Percival]

This patch adds an option,
\paper{ printAllHeaders = ##t }
which causes LilyPond to print all the headers for each \score in a 
\book.  Currently,
only the piece and opus are printed.  This is great for movements of a 
piece, but I have
several collections of pieces, for which I'd like all the headers 
printed (ie title, composer,
copyright, etc).

May I commit?  I'll add some docs as well, of course.

I've also attached my test case for the patch.

titling-init.ly.patch
Description: Binary data

foo.ly
Description: Binary data